Field of the Invention
[0001] The present invention relates to a golf ball, in particular, a golf ball traveling
a great flight distance and having an excellent approach performance and durability.
Description of the Related Art
[0002] As a method for improving a flight distance on driver shots, for example, there are
methods of using a core having high resilience and using a core having a hardness
distribution in which the hardness increases toward the surface of the core from the
center thereof. The former method has an effect of enhancing an initial speed, and
the latter method has an effect of a higher launch angle and a lower spin rate. A
golf ball having a higher launch angle and a low spin rate travels a great distance.
[0003] For example, Japanese Patent Publications Nos.
S61-37178 A,
2008-212681 A,
2008-523952 T and
2009-119256 A disclose a technique of enhancing resilience of the core. Japanese Patent Publications
Nos.
S61-37178 A and
S61-113475 A disclose a solid golf ball having an inner core where zinc acrylate as a co-crosslinking
agent, palmitic acid, stearic acid, or myristic acid as a co-crosslinking activator,
zinc oxide as another co-crosslinking activator, and a reaction rate retarder are
blended, with respect to 100 parts by weight of a rubber.
[0004] Japanese Patent Publication No.
2008-212681 A discloses a golf ball comprising, as a component, a molded and crosslinked product
obtained from a rubber composition essentially comprising a base rubber, a filler,
an organic peroxide, an α,β-unsaturated carboxylic acid and/or a metal salt thereof,
a copper salt of a saturated or unsaturated fatty acid.
[0005] Japanese Patent Publication No. 2008-523952 T discloses a golf ball, or a component thereof, molded from a composition comprising
a base elastomer selected from the group consisting of polybutadiene and mixtures
of polybutadiene with other elastomers, at least one metallic salt of an unsaturated
monocarboxylic acid, a free radical initiator, and a non-conjugated diene monomer.
[0006] Japanese Patent Publication No.
2009-119256 A discloses a method of manufacturing a golf ball, comprising preparing a masterbatch
of an unsaturated carboxylic acid and/or a metal salt thereof by mixing the unsaturated
carboxylic acid and/or the metal salt thereof with a rubber material ahead, using
the masterbatch to prepare a rubber composition containing the rubber material, and
employing a heated and molded product of the rubber composition as a golf ball component,
wherein the masterbatch of the unsaturated carboxylic acid and/or the metal salt thereof
comprises; (A) from 20 wt % to 100 wt % of a modified polybutadiene obtained by modifying
a polybutadiene having a vinyl content of from 0 to 2 %, a cis-1,4 bond content of
at least 80 % and active terminals, the active terminal being modified with at least
one type of alkoxysilane compound, and (B) from 80 wt % to 0 wt % of a diene rubber
other than (A) the above rubber component [the figures are represented by wt % in
the case that a total amount of (A) and (B) equal to 100 wt %] and (C) an unsaturated
carboxylic acid and/or a metal salt thereof.
[0007] For example, Japanese Patent Publications Nos.
H6-154357 A,
2008-194471 A,
2008-194473 A and
2010-253268 A disclose a core having a hardness distribution. Japanese Patent Publication No.
H6-154357 A discloses a two-piece golf ball comprising a core formed of a rubber composition
containing a base rubber, a co-crosslinking agent, and an organic peroxide, and a
cover covering said core, wherein the core has the following hardness distribution
according to JIS-C type hardness meter readings: (1) hardness at center: 58-73, (2)
hardness at 5 to 10 mm from center: 65-75, (3) hardness at 15 mm from center: 74-82,
(4) surface hardness: 76-84, wherein hardness (2) is almost constant within the above
range, and the relation (1)<(2)<(3)<(4) is satisfied.
[0008] Japanese Patent Publication No.
2008-194471 A discloses a solid golf ball comprising a solid core and a cover layer that encases
the core, wherein the solid core is formed of a rubber composition composed of 100
parts by weight of a base rubber that includes from 60 to 100 parts by weight of a
polybutadiene rubber having a cis-1,4 bond content of at least 60% and synthesized
using a rare-earth catalyst, from 0.1 to 5 parts by weight of an organic sulfur compound,
an unsaturated carboxylic acid or a metal salt thereof, an inorganic filler, and an
antioxidant; the solid core has a deformation from 2.0 mm to 4.0 mm, when applying
a load from an initial load of 10 kgf to a final load of 130 kgf and has the hardness
distribution shown in the following table.
Table 1
Hardness distribution in solid core |
Shore D harness |
Center |
30 to 48 |
Region located 4 mm from center |
34 to 52 |
Region located 8 mm from center |
40 to 58 |
Region located 12 mm from center (Q) |
43 to 61 |
Region located 2 to 3 mm inside of surface (R) |
36 to 54 |
Surface (S) |
41 to 59 |
Hardness difference [(Q)-(S)] |
1 to 10 |
Hardness difference [(S)-(R)] |
3 to 10 |
[0009] Japanese Patent Publication No.
2008-194473 A discloses a solid golf ball comprising a solid core and a cover layer that encases
the core, wherein the solid core is formed of a rubber composition composed of 100
parts by weight of a base rubber that includes from 60 to 100 parts by weight of a
polybutadiene rubber having a cis-1,4 bond content of at least 60% and synthesized
using a rare-earth catalyst, from 0.1 part to 5 parts by weight of an organic sulfur
compound, an unsaturated carboxylic acid or a metal salt thereof, and an inorganic
filler; the solid core has a deformation from 2.0 mm to 4.0 mm, when applying a load
from an initial load of 10 kgf to a final load of 130 kgf and has the hardness distribution
shown in the following table.
Table 2
Hardness distribution in solid core |
Shore D harness |
Center |
25 to 45 |
Region located 5 to 10mm from center |
39 to 58 |
Region located 15 mm from center |
36 to 55 |
Surface (S) |
55 to 75 |
Hardness difference between center and surface |
20 to 50 |
[0010] Japanese Patent Publication No.
2010-253268 A discloses a multi-piece solid golf ball comprising a core, an envelope layer encasing
the core, an intermediate layer encasing the envelope layer, and a cover which encases
the intermediate layer and has formed on a surface thereof a plurality of dimples,
wherein the core is formed primarily of a rubber material and has a hardness which
gradually increases from a center to a surface thereof, the hardness difference in
JIS-C hardness units between the core center and the core surface being at least 15
and, letting (I) be the average value for cross-sectional hardness at a position about
15 mm from the core center and at the core center and letting (II) be the cross-sectional
hardness at a position about 7.5 mm from the core center, the hardness difference
(I) - (II) in JIS-C units being within ± 2; and the envelope layer, intermediate layer
and cover have hardness which satisfy the condition: cover hardness>intermediate layer
hardness>envelope layer hardness.
[0011] US 2006/0017201 A1 relates to a cosmetically defect-free golf ball, which is prepared by a method comprising
the steps providing a golf ball precursor, filling a first set of mold halves with
a material comprising a saturated polyurethane and/or polyuria prepolymer as well
as a curing agent, lowering the golf ball precursor into the first set of mold halves
and heat-treating the golf ball precursor at vacuum in order to allow an exothermic
reaction of the polymer material, releasing the golf ball precursor from the vacuum
providing a partially covered golf ball precursor, filling the second set of mold
halves with the polymer material and mating the second set of mold halves with the
partially covered precursor to allow to complete an exothermic reaction of the material.
[0012] US 2012/008604 A1 discloses a golf ball having a core, a mid layer and a cover, wherein the core comprises
a center and an envelope layer, wherein the difference He-Ho between the JIS-C hardness
He at a surface of the core and the JIS-C hardness Ho at the central point of the
core is between 15 and 30, the JIS-C hardness Hc of the cover is less than the hardness
Ho and the ratio of the volume of the core to the volume of a phantom sphere of the
golf ball is at least 76 %.
[0013] US 2010/0273575 A1 relates to a multi-piece solid golf ball comprising a core, an envelope layer, an
intermediate layer and a cover, wherein the core has a hardness which gradually increases
from a center to the surface thereof, wherein the hardness difference in JIS-C hardness
units between the core center and the core surface is at least 15.
SUMMARY OF THE INVENTION
[0014] The present invention provides a golf ball traveling a great flight distance and
having an excellent approach performance and durability.
[0015] The present invention provides a golf ball comprising a spherical core composed of
a spherical inner core layer and an outer core layer, an intermediate layer disposed
outside the spherical core, and a cover disposed outside the intermediate layer, wherein
the hardness difference (Hs1-Ho) between the center hardness (Ho) of the spherical
inner core layer and the surface hardness (Hs1) thereof is 2 or less in JIS-C hardness;
the hardness difference (Hs2-Hb) between the hardness (Hb) at the border point between
the spherical inner core layer and the outer core layer and the surface hardness (Hs2)
of the spherical outer core layer is 20 or more in JIS-C hardness, the outer core
layer is such that R
2 of a linear approximation curve obtained from a least square method is 0.95 or higher,
when JIS-C hardness, which is measured at nine points obtained by dividing a thickness
of the outer core layer into equal parts having 12.5 % intervals in a radius direction
of the spherical core, is plotted against distance (%) from a border point between
the spherical inner core layer and the outer core layer; and the intermediate layer
has a slab hardness (Hm) which is higher than the slab hardness (Hc) of the cover.
[0016] That is, the gist of the golf ball of the present invention is that the golf ball
comprises the spherical core composed of the spherical inner core layer and the outer
core layer disposed outside the spherical inner core layer; and an intermediate layer
disposed outside the spherical core; and a cover disposed outside the intermediate
layer; wherein the spherical inner core has a low degree of an outer-hard inner-soft
structure, and the outer core layer is such that the hardness thereof increases linearly
or almost linearly from a boundary point between the inner core layer and outer core
layer toward the surface thereof, and the intermediate layer has a slab hardness (Hm)
which is higher than the slab hardness (Hc) of the cover. The present invention is
configured as described above, the present invention provides the golf ball traveling
a great flight distance and having an excellent approach performance and durability.
[0017] According to the present invention, it is possible to provide a golf ball traveling
a great flight distance and having an excellent approach performance and durability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018]
Fig. 1 is a partially cutaway sectional view showing the golf ball according to a
preferable embodiment of the present invention;
Fig. 2 is a partially cutaway sectional view showing the golf ball according to another
preferable embodiment of the present invention;
Fig. 3 is a graph showing the hardness distribution of the outer core layer;
Fig. 4 is a graph showing the hardness distribution of the outer core layer;
Fig. 5 is a graph showing the hardness distribution of the outer core layer;
Fig. 6 is a graph showing the hardness distribution of the outer core layer;
Fig. 7 is a graph showing the hardness distribution of the outer core layer;
Fig. 8 is a graph showing the hardness distribution of the outer core layer;
Fig. 9 is a graph showing the hardness distribution of the outer core layer;
Fig. 10 is a graph showing the hardness distribution of the outer core layer;
Fig. 11 is a graph showing the hardness distribution of the outer core layer;
Fig. 12 is a graph showing the hardness distribution of the outer core layer;
Fig. 13 is a graph showing the hardness distribution of the outer core layer;
Fig. 14 is a graph showing the hardness distribution of the outer core layer;
Fig. 15 is a graph showing the hardness distribution of the outer core layer;
Fig. 16 is a graph showing the hardness distribution of the outer core layer;
Fig. 17 is a graph showing the hardness distribution of the outer core layer;
Fig. 18 is a graph showing the hardness distribution of the outer core layer;
Fig. 19 is a graph showing the hardness distribution of the outer core layer;
Fig. 20 is a graph showing the hardness distribution of the outer core layer;
Fig. 21 is a graph showing the hardness distribution of the outer core layer;
Fig. 22 is a graph showing the hardness distribution of the outer core layer;
Fig. 23 is a graph showing the hardness distribution of the outer core layer;
Fig. 24 is a graph showing the hardness distribution of the outer core layer;
Fig. 25 is a graph showing the hardness distribution of the outer core layer;
Fig. 26 is a graph showing the hardness distribution of the outer core layer;
Fig. 27 is a graph showing the hardness distribution of the outer core layer;
Fig. 28 is a graph showing the hardness distribution of the outer core layer;
Fig. 29 is a graph showing the hardness distribution of the outer core layer;
Fig. 30 is a graph showing the hardness distribution of the outer core layer;
Fig. 31 is a graph showing the hardness distribution of the outer core layer;
Fig. 32 is a graph showing the hardness distribution of the outer core layer;
Fig. 33 is a graph showing the hardness distribution of the outer core layer;
Fig. 34 is a graph showing the hardness distribution of the outer core layer;
Fig. 35 is a graph showing the hardness distribution of the outer core layer;
Fig. 36 is a graph showing the hardness distribution of the outer core layer;
Fig. 37 is a graph showing the hardness distribution of the outer core layer;
Fig. 38 is a graph showing the hardness distribution of the outer core layer;
Fig. 39 is a graph showing the hardness distribution of the outer core layer;
Fig. 40 is a graph showing the hardness distribution of the outer core layer;
Fig. 41 is a graph showing the hardness distribution of the outer core layer; and
Fig. 42 is a graph showing the hardness distribution of the outer core layer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0019] The present invention provides a golf ball comprising a spherical core composed of
a spherical inner core layer and an outer core layer, an intermediate layer disposed
outside the spherical core, and a cover disposed outside the intermediate layer, wherein
a hardness difference (Hs1-Ho) between a center hardness (Ho) of the spherical inner
core layer and a surface hardness (Hs1) thereof is 5 or less in JIS-C hardness; the
hardness difference (Hs2-Hb) between the hardness (Hb) at the boarder point between
the spherical inner core layer and the outer core layer and the surface hardness (Hs2)
of the spherical outer core layer is 20 or more in JIS-C hardness, the outer core
layer is such that R
2 of a linear approximation curve obtained from a least square method is 0.95 or higher,
when JIS-C hardness, which is measured at nine points obtained by dividing a thickness
of the outer core layer into equal parts having 12.5 % intervals in a radius direction
of the spherical core, is plotted against distance (%) from a border point between
the spherical inner core layer and the outer core layer; and the intermediate layer
has a slab hardness (Hm) which is higher than a slab hardness (Hc) of the cover.
(1) Golf Ball Construction
[0020] The golf ball of the present invention is not limited, as long as it comprises a
spherical core composed of a spherical inner core layer and an outer core layer, an
intermediate layer disposed outside the spherical core, and a cover disposed outside
the intermediate layer. Hereinafter, the golf ball of the present invention will be
described based on preferred embodiments, referring to the accompanying drawings appropriately.
[0021] The inner core layer has a spherical shape. The inner core has a hardness difference
(Hs1-Ho) between a surface hardness (Hs1) thereof and a center hardness (Ho) thereof
of 5 or less, preferably 4 or less, and more preferably 2 or less in JIS-C hardness.
If the hardness difference (Hs1-Ho) is more than 5 in JIS-C hardness, the resilience
of the golf ball deteriorates, and thus the initial velocity of the golf ball when
hit is decreased. The lower limit of the above hardness difference is not limited,
but the hardness difference is preferably 0 or more, and more preferably 1 or more
JIS-C hardness.
[0022] The inner core layer preferably has the center hardness (Ho) of 40 or more, more
preferably 50 or more, and even more preferably 60 or more in JIS-C hardness. If the
center hardness is 40 or more in JIS-C hardness, the resilience improves. Further,
from the aspect of suppression of the spin upon driver shots, the inner core layer
preferably has the center hardness (Ho) of 80 or less, more preferably 76 or less,
and even more preferably 72 or less in JIS-C hardness.
[0023] The inner core layer preferably has a surface hardness (Hs1) of 50 or more, more
preferably 55 or more, and even more preferably 60 or more in JIS-C hardness. If the
surface hardness is 50 or more in JIS-C hardness, the resilience improves. From the
aspect of reducing the spin rate upon driver shots, the inner core layer preferably
has the surface hardness (Hs1) of 80 or less, more preferably 75 or less, and even
more preferably 70 or less in JIS-C hardness.
[0024] The inner core layer preferably has a diameter of 10.0 mm or more, more preferably
12.0 mm or more, and even more preferably 14.0 mm or more. If the inner core layer
has the diameter of 10.0 mm or more, the spin rate on driver shots is reduced. The
inner core layer preferably has a diameter of 25.0 mm or less, more preferably 22.0
mm or less, and even more preferably 19.0 mm or less. If the inner core layer has
the diameter of 25.0 mm or less, the golf ball has the improved resilience performance.
[0025] The outer core layer is disposed outside the inner core layer. The outer core layer
is preferably formed to cover the whole inner core layer.
[0026] The outer core layer is such that R
2 of a linear approximation curve obtained from a least square method is 0.95 or higher,
when JIS-C hardness, which is measured at nine points obtained by dividing a thickness
of the outer core layer in a radius direction of the spherical core into equal parts
having 12.5% intervals therebetween, is plotted against distance (%) from the boundary
point between the inner core layer and the outer core layer. If R
2 is 0.95 or more, the linearity of the hardness distribution of the outer core layer
is enhanced, the spin rate on driver shots is reduced, thereby providing a great flight
distance.
[0027] The hardness of the outer core layer is JIS-C hardness measured at nine points obtained
by dividing a thickness of the outer core layer in a radius direction of the spherical
core into equal parts having 12.5% intervals. That is, JIS-C hardness is measured
at nine points, namely at the innermost point of the outer core layer (0%: the border
point between the inner core layer and the outer core layer), and at distances of
12.5%, 25%, 37.5%, 50%, 62.5%, 75%, 87.5%, 100% (surface hardness Hs2 of the spherical
core) from the border point between the inner core layer and the outer core layer.
Next, the measurement results are plotted to make a graph having JIS-C hardness as
a vertical axis and distances (%) from the border point as a horizontal axis. In the
present invention, R
2 of a linear approximation curve obtained from this graph by the least square method
is preferably 0.95 or higher. R
2 of the linear approximation curve obtained by the least square method indicates the
linearity of the obtained plot. In the present invention, R
2 of 0.95 or more means that the outer core layer has the hardness distribution where
the hardness increases linearly or almost linearly. If the outer core layer having
the hardness distribution where the hardness increases linearly or almost linearly
is used for the golf ball, the spin rate on driver shots decrease. As a result, the
flight distance on driver shots increases. R
2 of the linear approximation curve is preferably 0.96 or more, more preferably 0.97
or more. The higher linearity provides a greater flight distance on driver shots.
[0028] The hardness difference (Hs2-Hb) between the surface hardness (Hs2) of the outer
core layer and the hardness (Hb) at the border point between the outer core layer
and the inner core layer is 20 or more, preferably 22 or more, and more preferably
24 or more, and is preferably 45 or less, more preferably 40 or less, even more preferably
35 or less in JIS-C hardness. If the hardness difference (Hs2-Hb) is 20 or more in
JIS-C hardness, it is possible to further reduce the spin rate on driver shots. If
the hardness difference (Hs2-Hb) is 45 or less, the durability does not deteriorate.
In the present invention, it is noted that the surface hardness (Hs2) of the spherical
core is same as the surface hardness of the outer core layer.
[0029] The surface hardness (Hs2) of the outer core layer is preferably 80 or more, more
preferably 82 or more, and even more preferably 84 or more in JIS-C hardness. If the
surface hardness (Hs2) of the outer core layer is 80 or more in JIS-C hardness, the
spin rate on driver shots are further reduced. From the aspect of the durability,
the surface hardness (Hs2) of the outer core layer is preferably 96 or less, more
preferably 94 or less, and even more preferably 92 or less in JIS-C hardness.
[0030] The hardness (Hb) at the innermost point (a border point between the outer core layer
and the inner core layer) of the outer core layer is preferably 50 or more, more preferably
55 or more, and even more preferably 60 or more in JIS-C hardness. If the hardness
at the innermost point of the outer core layer is 50 or more in JIS-C hardness, the
ball speed when hit improves. From the aspect of lowering the spin rate on driver
shots, the hardness (Hb) at the innermost point of the outer core layer is preferably
80 or less, more preferably 75 or less, and even more preferably 70 or less in JIS-C
hardness.
[0031] The outer core layer preferably has a thickness of 6 mm or more, more preferably
8 mm or more, and even more preferably 11 mm or more, and preferably has a thickness
of 16 mm or less, more preferably 15 mm or less, and even more preferably 13 mm or
less. If the thickness is 6 mm or more, it is possible to suppress the decrease in
the ball speed when hit. If the thickness is 16 mm or less, it is possible to enhance
the effect of lowering the spin rate.
[0032] The spherical core preferably has a hardness difference (Hs2-Ho) between a surface
hardness thereof (Hs2) (which is same as the surface hardness of the outer core layer)
and a center hardness thereof (Ho) (same as the center hardness of the inner core
layer) of 20 or more, more preferably 21 or more, even more preferably 22 or more,
and preferably has a hardness difference of 45 or less, more preferably 40 or less,
even more preferably 35 or less in JIS-C hardness. If the hardness difference between
the center hardness of the spherical core and the surface hardness thereof is within
the above range, the golf ball having a great flight distance due to the high launch
angle and low spin rate is obtained.
[0033] The spherical core preferably has a diameter of 36.0 mm or more, more preferably
37.0 mm or more, and even more preferably 38.0 mm or more. If the spherical core has
the diameter of 36.0 mm or more, it is possible to make the inner core layer have
a greater diameter, thereby improving the resilience performance of the golf ball.
The spherical core preferably has a diameter of 40.6 mm or less, more preferably 40.3
mm or less, and even more preferably 40.0 mm or less. If the spherical core has the
diameter of 40.6 mm or less, it is possible to suppress a reduction in durability.
[0034] When the spherical core has a diameter from 36.0 mm to 40.6 mm, a compression deformation
amount (shrinking deformation amount of the spherical core along the compression direction)
of the spherical core when applying a load from an initial load of 98 N to a final
load of 1275 N is preferably 2.2 mm or more, more preferably 2.5 mm or more, and is
preferably 4.0 mm or less, more preferably 3.5 mm or less. If the compression deformation
amount is 2.2 mm or more, the shot feeling of the golf ball becomes better. If the
compression deformation amount is 4.0 mm or less, the resilience of the golf ball
becomes better.
[0035] The golf ball of the present invention comprises the intermediate layer disposed
outside the spherical core and the cover disposed outside the intermediate layer.
The intermediate layer is formed between the spherical core and the cover, and is
composed of at least one layer. The intermediate layer may have two or more layers.
The cover is formed as the outermost layer of the golf ball body.
[0036] The golf ball of the present invention includes, for example, a four-piece golf ball
comprising a spherical core composed of a spherical inner core layer and an outer
core layer, an intermediate layer disposed outside the spherical core and an cover
outside the intermediate layer; and a multi-piece golf ball (five-piece or more) comprising
a spherical core composed of a spherical inner core layer and an outer core layer,
two or more intermediate layers disposed outside the spherical core, and a cover disposed
outside the intermediate layer. In the followings, with respect to the embodiment
of the four-piece golf ball, the present invention will be described referring to
"preferable embodiment A," and with respect to the embodiment of the multi-piece golf
ball (five-piece or more), the present invention will be described referring to "preferable
embodiment B."
[0037] In the preferable embodiment A, the golf ball of the present invention comprises
a single-layered intermediate layer disposed outside the spherical core and a cover
disposed outside the intermediate layer. Fig. 1 is a partially cutaway sectional view
showing the golf ball 2 according to the preferable embodiment A of the present invention.
The golf ball 2 comprises a spherical core 7 composed of a spherical inner core layer
4 and an outer core layer 6 disposed outside the spherical inner core layer 4, a single-layered
intermediate layer 8 disposed outside the spherical core 7, and a cover 12 disposed
outside the intermediate layer 8. A reinforcing layer 10 may be disposed between the
intermediate layer 8 and the cover 12 in order to improve adhesion between the intermediate
layer 8 and the cover 12. A plurality of dimples 14 are formed on a surface of the
cover 12. Other portions than dimples 14 on the surface of the cover 12 are referred
to as "land 16". The golf ball 2 is provided with a paint layer and a mark layer outside
the cover, but these layers are not depicted.
[0038] In the preferable embodiment A, the slab hardness (Hm) of the intermediate layer
is higher than the slab hardness (Hc) of the cover. This configuration strikes a balance
between a great flight distance and an approach performance. The hardness difference
(Hm-Hc) between the slab hardness (Hm) of the intermediate layer and the slab hardness
(Hc) of the cover is preferably 30 or more, more preferably 32 or more, even more
preferably 34 or more, and is preferably 40 or less, more preferably 38 or less, even
more preferably 36 or less in Shore D hardness. If the hardness difference (Hm-Hc)
falls within the above range, it is possible to produce a low spin rate on driver
shots and high spin rate on iron shots. Further, in the case that the intermediate
layer is composed of at least two layers, the hardness difference between the cover
and the intermediate layer adjacent to the cover (the outermost intermediate layer)
is adjusted to fall within the above range.
[0039] In the preferable embodiment A, the intermediate layer preferably has a slab hardness
(Hm) of 55 or more, more preferably 60 or more, even more preferably 63 or more, and
preferably has a slab hardness (Hm) of 70 or less, more preferably 68 or less, even
more preferably 67 or less in Shore D hardness. If the slab hardness of the intermediate
layer is 55 or more in Shore D hardness, the degree of outer-hard inner-soft of the
golf ball (except the cover) is enhanced, thereby producing a much lower spin rate
on driver shots. If the slab hardness of the intermediate layer is 70 or less in Shore
D hardness, the approach performance becomes much better.
[0040] In the preferable embodiment A, the intermediate layer preferably has a thickness
of 0.5 mm or more, more preferably 0.7 mm or more, and even more preferably 0.8 mm
or more. If the thickness is 0.5 mm or more, the durability becomes better. The intermediate
layer preferably has a thickness of 1.6 mm or less, more preferably 1.3 mm or less,
and even more preferably 1.1 mm or less. If the thickness is 1.6 mm or less, it is
possible to relatively enlarge a diameter of the spherical core, and thus the resilience
of the golf ball improves.
[0041] In the preferable embodiment B, the golf ball of the present invention comprises
a first intermediate layer disposed outside the spherical core, a second intermediate
layer disposed outside the first intermediate layer, and a cover disposed outside
the second intermediate layer. The intermediate layers are formed between the spherical
core and the cover, and composed of at least two layers having the first intermediate
layer and the second intermediate layer. The intermediate layer may have three or
more layers. In case of three or more intermediate layers, the intermediate layer
disposed on the innermost side of the intermediate layers is referred to as "the first
intermediate layer" and the intermediate layer disposed on the outermost side of the
intermediate layers is referred to as "the second intermediate layer." The cover is
formed as the outermost layer of the golf ball body.
[0042] Fig. 2 is a partially cutaway sectional view showing the golf ball 2 according to
the preferable embodiment B of the present invention. The golf ball 2 comprises a
spherical core 7 composed of a spherical inner core 4 and an outer core layer 6 disposed
outside the spherical inner core 4, a first intermediate layer 8 disposed outside
the spherical core 7, and a second intermediate layer 9 disposed outside the first
intermediate layer 8, and a cover 12 disposed outside the second intermediate layer
9. A reinforcing layer 10 may be disposed between the second intermediate layer 9
and the cover 12 in order to improve adhesion between the second intermediate layer
9 and the cover 12. A plurality of dimples 14 are formed on a surface of the cover
12. Other portions than dimples 14 on the surface of the cover 12 are referred to
as "land 16". The golf ball 2 is provided with a paint layer and a mark layer outside
the cover, but these layers are not depicted.
[0043] The hardness difference (Hm2-Hm1) between the slab hardness (Hm1) of the first intermediate
layer and the slab hardness (Hm2) of the second intermediate layer is preferably 8
or more, more preferably 14 or more, even more preferably 16 or more, and is preferably
35 or less, more preferably 30 or less, even more preferably 25 or less in Shore D
hardness. If the hardness difference (Hm2-Hm1) falls within the above range, since
the degree of outer-hard inner-soft of the golf ball (except the cover) is enhanced,
it is possible to produce a lower spin rate on driver shots. Further, the spin rate
on approach shots increases, and thus the approach performance is enhanced.
[0044] In the preferable embodiment B, the first intermediate layer preferably has a slab
hardness (Hm1) of 30 or more, more preferably 40 or more, even more preferably 45
or more, and preferably has a slab hardness (Hm1) of 60 or less, more preferably 54
or less, even more preferably 52 or less in Shore D hardness. If the slab hardness
of the first intermediate layer is 30 or more in Shore D hardness, it is possible
to lower the spin rate on driver shots. If the slab hardness of the first intermediate
layer is 60 or less in Shore D hardness, the approach performance becomes much better.
[0045] In the preferable embodiment B, the second intermediate layer preferably has a slab
hardness (Hm2) of 55 or more, more preferably 60 or more, even more preferably 63
or more, and preferably has a slab hardness (Hm2) of 70 or less, more preferably 68
or less, even more preferably 67 or less in Shore D hardness. If the slab hardness
of the second intermediate layer is 55 or more in Shore D hardness, the degree of
outer-hard inner-soft of the golf ball (except the cover) is enhanced, thereby producing
a much lower spin rate on driver shots. If the slab hardness of the second intermediate
layer is 70 or less in Shore D hardness, the approach performance becomes much better.
[0046] In case of three or more intermediate layers in the preferable embodiment B of the
present invention, the hardness of the intermediate layer disposed between the first
intermediate layer and the second intermediate layer is preferably higher than the
hardness of the first intermediate layer and is preferably lower than the hardness
of the second intermediate layer. Further, the hardness of the intermediate layers
is preferably designed as follows. The first intermediate layer has the lowest hardness,
the intermediate layers disposed outside the first intermediate layer have the hardness
which gradually increases from the inside to the outside, and the second intermediate
layer has the highest hardness.
[0047] In the preferable embodiment B, the first and second intermediate layers preferably
have a thickness of 0.5 mm or more, more preferably 0.7 mm or more, and even more
preferably 0.8 mm or more, respectively. If the thickness of the first and second
intermediate layers is 0.5 mm or more, the durability becomes better. The first and
second intermediate layers preferably have a thickness of 1.5 mm or less, more preferably
1.2 mm or less, and even more preferably 1.1 mm or less, respectively. If the thickness
of the intermediate layer is 1.5 mm or less, it is possible to relatively enlarge
a diameter of the spherical core, and thus the resilience of the golf ball improves.
[0048] In the preferable embodiment B, the hardness difference (Hm2-Hc) between the slab
hardness (Hm2) of the second intermediate layer and the slab hardness (Hc) of the
cover is preferably 30 or more, more preferably 32 or more, even more preferably 34
or more, and is preferably 45 or less, more preferably 42 or less, even more preferably
38 or less in Shore D hardness. If the hardness difference (Hm2-Hc) falls within the
above range, it is possible to produce a low spin rate on driver shots and high spin
rate on iron shots.
[0049] The golf ball of the present invention has a cover disposed outside the intermediate
layer.
[0050] The cover preferably has a slab hardness (Hc) of 48 or less, more preferably 40 or
less, even more preferably 32 or less in Shore D hardness. If the slab hardness of
the cover is 48 or less in Shore D hardness, the spin rate on approach shots increases,
thereby enhancing controllability. The cover preferably has a slab hardness (Hc) of
20 or more, more preferably 24 or more, even more preferably 28 or more in Shore D
hardness. If the slab hardness of the cover is 20 or more in Shore D hardness, the
abrasion resistance of the cover improves.
[0051] The cover preferably has a thickness of 0.8 mm or less, more preferably 0.7 mm or
less, even more preferably 0.6 mm or less. If the thickness is 0.8 mm or less, the
spin rate on driver shots is further reduced. The cover preferably has a thickness
of 0.1 mm or more, more preferably 0.2 mm or more, and even more preferably 0.3 mm
or more. If the cover is too thin, it tends to be difficult to mold the cover.
[0052] The concave portions called "dimple" are usually formed on the surface of the cover.
The total number of the dimples is preferably 200 or more and 500 or less. If the
total number is less than 200, the dimple effect is hardly obtained. On the other
hand, if the total number exceeds 500, the dimple effect is hardly obtained because
the size of the respective dimples is small. The shape (shape in a plan view) of dimples
includes, for example, without limitation, a circle, polygonal shapes such as roughly
triangular shape, roughly quadrangular shape, roughly pentagonal shape, roughly hexagonal
shape, and another irregular shape. The shape of the dimples is employed solely or
at least two of them may be used in combination.
[0053] The golf ball of the present invention may have a reinforcing layer between the intermediate
layer and the cover. The reinforcing layer adheres firmly to the intermediate layer
as well as to the cover. The reinforcing layer suppresses delamination of the cover
from the intermediate layer. In particular, when the golf ball with a thin cover is
hit with an edge of a clubface, a wrinkle easily generates. The reinforcing layer
suppresses the generation of the wrinkle.
[0054] From the aspect of suppressing the wrinkle, the reinforcing layer preferably has
a thickness of 3 µm or more, and more preferably 5 µm or more. In order to facilitate
the formation of the reinforcing layer, the reinforcing layer preferably has a thickness
of 15 µm or less, more preferably 12 µm or less, and even more preferably 10 µm or
less. The thickness is measured by observing a cross section of the golf ball with
a microscope. When the intermediate layer has concavities and convexities on its surface
by surface roughening, the thickness of the reinforcing layer is measured at the top
of the convex part.
[0055] From the aspect of suppressing the wrinkle, the reinforcing layer preferably has
a pencil hardness of 4B or harder, and more preferably B or harder. From the aspect
of reducing the loss of the power transmission from the cover to the intermediate
layer upon a hit of the golf ball, the reinforcing layer preferably has a pencil hardness
or 3H or softer. The pencil hardness is measured according to the standard of "JIS
K5400".
[0056] When the golf ball of the present invention has a diameter in a range from 40 mm
to 45 mm, a compression deformation amount of the golf ball (shrinking amount of the
golf ball in the compression direction thereof) when applying a load from an initial
load of 98 N to a final load of 1275 N to the golf ball is preferably 1.8 mm or more,
more preferably 2.0 mm or more, even more preferably 2.2 mm or more, even more preferably
2.3 mm or more, most preferably 2.4 mm or more, and is preferably 3.6 mm or less,
more preferably 3.0 mm or less. If the compression deformation amount is 1.8 mm or
more, the golf ball does not become excessively hard, and thus exhibits the good shot
feeling. On the other hand, if the compression deformation amount is 3.6 mm or less,
the resilience is enhanced.
[0057] It is preferred that a paint film is formed on a surface of the golf ball body. The
paint film preferably has a thickness of, but not limited to, 5 µm or more, and more
preferably 7 µm or more, and preferably has a thickness of 50 µm or less, and more
preferably 40 µm or less, even more preferably 30 µm or less. If the thickness is
less than 5 µm, the paint film is easy to wear off due to continued use of the golf
ball, and if the thickness is more than 50 µm, the effect of the dimples is reduced,
resulting in lowering flying performance of the golf ball.
(2) Outer Core Layer Rubber Composition
[0058] The outer core layer of the golf ball of the present invention is preferably formed
from an outer core layer rubber composition containing (a) a base rubber, (b1) an
α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or (b2) a metal salt
of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms as (b) a co-crosslinking
agent, (c) a crosslinking initiator, and (d) an acid and/or a salt thereof. The outer
core layer formed from the above rubber composition tends to have a hardness distribution
where the hardness increases linearly or almost linearly from a boundary point between
the inner core layer and the outer core layer toward the surface of the outer core
layer.
[0059] The reason why the outer core layer formed from the above rubber composition has
the hardness distribution where the hardness increases linearly or almost linearly
from the boundary point between the outer core layer and the inner core layer toward
the surface of the outer core layer is considered as follows. When molding the outer
core layer, the internal temperature of the outer core layer is high at the inside
of the outer core layer and decreases toward the surface of the outer core layer,
since reaction heat from a crosslinking reaction of the base rubber accumulates at
the inside of the outer core layer. (d) The acid and/or the salt thereof reacts with
(b) the metal salt of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms,
when molding the outer core layer. That is, (d) the acid and/or the salt thereof exchanges
the cation with the metal salt of the α,β-unsaturated carboxylic acid having 3 to
8 carbon atoms, thereby breaking a metal crosslinking by the metal salt of the α,β-unsaturated
carboxylic acid having 3 to 8 carbons atoms. This cation exchange reaction readily
occurs at the inside of the outer core layer where the temperature is high, and less
occurs toward the surface of the outer core layer. In other words, the breaking of
the metal crosslinking readily occurs at the inside of the outer core layer, but less
occurs toward the surface of the outer core layer. As a result, it is conceivable
that since a crosslinking density in the outer core layer increases from the boundary
point between the outer core layer and inner core layer toward the surface of the
outer core layer, the hardness of the outer core layer increases linearly or almost
linearly from the boundary point between the outer core layer and the inner core layer
toward the surface of the outer core layer. In addition, by using (e) the organic
sulfur compound together with (d) the acid and/or the salt thereof, the slope of the
hardness distribution can be controlled, and the degree of the outer-hard and inner-soft
structure of the core can be further enhanced.
[0060] As (a) the base rubber used in the present invention, natural rubber and/or synthetic
rubber can be used. For example, polybutadiene rubber, natural rubber, polyisoprene
rubber, styrene polybutadiene rubber, ethylene-propylene-diene rubber (EPDM), or the
like can be used. These rubbers may be used solely or two or more of these rubbers
may be used in combination. Among them, typically preferred is the high cis-polybutadiene
having a cis-1,4 bond in a proportion of 40 % or more, more preferably 80 % or more,
even more preferably 90 % or more in view of its superior resilience property.
[0061] The high-cis polybutadiene preferably has a 1,2-vinyl bond in a content of 2 mass
% or less, more preferably 1.7 mass % or less, and even more preferably 1.5 mass %
or less. If the content of 1,2-vinyl bond is excessively high, the resilience may
be lowered.
[0062] The high-cis polybutadiene preferably includes one synthesized using a rare earth
element catalyst. When a neodymium catalyst, which employs a neodymium compound of
a lanthanum series rare earth element compound, is used, a polybutadiene rubber having
a high content of a cis-1,4 bond and a low content of a 1,2-vinyl bond is obtained
with excellent polymerization activity. Such a polybutadiene rubber is particularly
preferred.
[0063] The high-cis polybutadiene preferably has a Mooney viscosity (ML
1+4 (100 °C)) of 30 or more, more preferably 32 or more, even more preferably 35 or more,
and preferably has a Mooney viscosity (ML
1+4 (100 °C)) of 140 or less, more preferably 120 or less, even more preferably 100 or
less, and most preferably 80 or less. It is noted that the Mooney viscosity (ML
1+4 (100 °C)) in the present invention is a value measured according to JIS K6300 using
an L rotor under the conditions of: a preheating time of 1 minute; a rotor revolution
time of 4 minutes; and a temperature of 100 °C.
[0064] The high-cis polybutadiene preferably has a molecular weight distribution Mw / Mn
(Mw: weight average molecular weight, Mn: number average molecular weight) of 2.0
or more, more preferably 2.2 or more, even more preferably 2.4 or more, and most preferably
2.6 or more, and preferably has a molecular weight distribution Mw / Mn of 6.0 or
less, more preferably 5.0 or less, even more preferably 4.0 or less, and most preferably
3.4 or less. If the molecular weight distribution (Mw / Mn) of the high-cis polybutadiene
is excessively low, the processability may deteriorate. If the molecular weight distribution
(Mw / Mn) of the high-cis polybutadiene is excessively high, the resilience may be
lowered. It is noted that the measurement of the molecular weight distribution is
conducted by gel permeation chromatography ("HLC-8120GPC", manufactured by Tosoh Corporation)
using a differential refractometer as a detector under the conditions of column: GMHHXL
(manufactured by Tosoh Corporation), column temperature: 40 °C, and mobile phase:
tetrahydrofuran, and calculated by converting based on polystyrene standard.
[0065] Next, (b) the co-crosslinking agent will be described. (b) The co-crosslinking agent
includes (b1) an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or
(b2) a metal salt of theα,β-unsaturated carboxylic acid having 3 to 8 carbon atoms.
Hereinafter, (b1) the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or
(b2) the metal salt thereof sometimes may be merely referred to as "(b) an α,β-unsaturated
carboxylic acid having 3 to 8 carbon atoms and/or a metal salt thereof".
(b) The α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or a metal
salt thereof is blended as a co-crosslinking agent in the rubber composition and has
an action of crosslinking a rubber molecule by graft polymerization to a base rubber
molecular chain. In the case that the rubber composition used in the present invention
contains only (b1) the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms
as the co-crosslinking agent, the rubber composition preferably contains (f) a metal
compound which will be described later. Neutralizing (b1) the α,β-unsaturated carboxylic
acid having 3 to 8 carbon atoms with (f) the metal compound in the rubber composition
provides substantially the same effect as using the metal salt of the α,β-unsaturated
carboxylic acid having 3 to 8 carbon atoms as the co-crosslinking agent. Further,
in the case of using (b1) the α,β-unsaturated carboxylic acid having 3 to 8 carbon
atoms and (b2) the metal salt thereof in combination, (f) the metal compound may be
used.
(b1) The α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms includes, for
example, acrylic acid, methacrylic acid, fumaric acid, maleic acid, crotonic acid,
and the like.
[0066] Examples of the metals constituting (b2) the metal salts of the α,β-unsaturated carboxylic
acid having 3 to 8 carbon atoms include: monovalent metal ions such as sodium, potassium,
lithium or the like; divalent metal ions such as magnesium, calcium, zinc, barium,
cadmium or the like; trivalent metal ions such as aluminum ion or the like; and other
metal ions such as tin, zirconium or the like. The above metal ions can be used solely
or as a mixture of at least two of them. Among these metal ions, divalent metal ions
such as magnesium, calcium, zinc, barium, cadmium or the like are preferable. Use
of the divalent metal salts of the α,β-unsaturated carboxylic acid having 3 to 8 carbon
atoms easily generates a metal crosslinking between the rubber molecules. Especially,
as the divalent metal sat, zinc acrylate is preferable, because zinc acrylate enhances
the resilience of the resultant golf ball. (b) The α,β-unsaturated carboxylic acid
having 3 to 8 carbon atoms and/or a metal salt thereof may be used solely or in combination
at least two of them.
[0067] The content of (b) the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms
and/or the metal salt thereof is preferably 15 parts by mass or more, more preferably
20 parts by mass or more, and is preferably 50 parts by mass or less, more preferably
45 parts by mass or less, even more preferably 40 parts by mass or less, with respect
to 100 parts by mass of (a) the base rubber. If the content of (b) the α,β-unsaturated
carboxylic acid having 3 to 8 carbon atoms and/or the metal salt thereof is less than
15 parts by mass, the content of (c) the crosslinking initiator which will be described
below must be increased in order to obtain the appropriate hardness of the constituting
member formed from the rubber composition, which tends to cause the lower resilience.
On the other hand, if the content of (b) the α,β-unsaturated carboxylic acid having
3 to 8 carbon atoms and/or the metal salt thereof exceeds 50 parts by mass, the constituting
member formed from the rubber composition becomes excessively hard, which may cause
the lower shot feeling.
(c) The crosslinking initiator is blended in order to crosslink (a) the base rubber
component. As (c) the crosslinking initiator, an organic peroxide is preferred. Specific
examples of the organic peroxide include organic peroxides such as dicumyl peroxide,
1,1-bis(t-butylperoxy)-3,3,5-trimethylcyclohexane, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane,
and di-t-butyl peroxide. These organic peroxides may be used solely or two or more
of these organic peroxides may be used in combination. Among them, dicumyl peroxide
is preferably used.
[0068] The content of (c) the crosslinking initiator is preferably 0.2 part by mass or more,
and more preferably 0.5 part by mass or more, and is preferably 5.0 parts by mass
or less, and more preferably 2.5 parts by mass or less, with respect to 100 parts
by mass of (a) the base rubber. If the content of (c) the crosslinking initiator is
less than 0.2 part by mass, the constituting member formed from the rubber composition
becomes too soft, and thus the golf ball may have the lower resilience. If the content
of (c) the crosslinking initiator exceeds 5.0 parts by mass, the amount of (b) the
co-crosslinking agent must be decreased in order to obtain the appropriate hardness
of the constituting member formed from the rubber composition, resulting in the insufficient
resilience and lower durability of the golf ball.
[0069] Next, (d) the acid and/or the salt thereof will be described. It is considered that
(d) the acid and/or the salt thereof has an action of breaking the metal crosslinking
by the metal salt of (b) the α,β-unsaturated carboxylic acid having 3 to 8 carbon
atoms in the outer core layer, when molding the outer core layer.
(d) The acid and/or the salt thereof may include any one of an aliphatic acid and/or
a salt thereof and an aromatic acid and/or a salt thereof, as long as it exchanges
the cation component with the metal salt of the α,β-unsaturated carboxylic acid having
3 to 8 carbon atoms. As (d) the acid and/or the salt thereof, for example, preferred
is a protonic acid and/ or a salt thereof. The protonic acid includes oxo acids such
as a carboxylic acid, a sulfonic acid, and a phosphoric acid; and hydroacids such
as hydrochloric acid, hydrofluoric acid or the like. Preferred of the acids is an
oxo acid, more preferred is a carboxylic acid. That is, (d) the acid and/or the salt
thereof preferably includes a carboxylic acid and/or a salt thereof.
(d) The acid and/or the salt thereof may include any one of an aliphatic carboxylic
acid (sometimes may be merely referred to as "fatty acid" in the present invention)
and/or a salt thereof and an aromatic carboxylic acid and/or a salt thereof, and preferred
is the aliphatic carboxylic acid and/or the salt thereof. (d) The carboxylic acid
and/or the salt thereof preferably includes a carboxylic acid having 1 to 30 carbon
atoms and/or a salt thereof, more preferably a carboxylic acid having 4 to 30 carbon
atoms and/or a salt thereof, and even more preferably a carboxylic acid having 5 to
25 carbon atoms and/or a salt thereof. (d) The carboxylic acid and/or the salt thereof
does not include (b) the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms
and/or the metal salt thereof used as the co-crosslinking agent.
[0070] The fatty acid may be either a saturated fatty acid or an unsaturated fatty acid;
however, a saturated fatty acid is preferable. Specific examples of the saturated
fatty acids (IUPAC name) are methanoic acid (C1), ethanoic acid (C2), propanoic acid
(C3), butanoic acid (C4), pentanoic acid (C5), hexanoic acid (C6), heptanoic acid
(C7), octanoic acid (C8), nonanoic acid (C9), decanoic acid (C10), undecanoic acid
(C11), dodecanoic acid (C12), tridecanoic acid (C13), tetradecanoic acid (C14), pentadecanoic
acid (C15), hexadecnoic acid (C16), heptadecanoic acid (C17), octadecanoic acid (C18),
nonadecanoic acid (C19), icosanoic acid (C20), henicosanoic acid (C21), docosanoic
acid (C22), tricosanoic acid (C23), tetracosanoic acid (C24), pentacosanoic acid (C25),
hexacosanoic acid (C26), heptacosanoic acid (C27), octacosanoic acid (C28), nonacosanoic
acid (C29), triacontanoic acid (C30).
[0071] Specific examples of the unsaturated fatty acid (IUPAC) are ethenoic acid (C2), propenoic
acid (C3), butenoic acid (C4), pentenoic acid (C5), hexenoic acid (C6), heptenoic
acid (C7), octenoic acid (C8), nonenoic acid (C9), decenoic acid (C10), undecenoic
acid (C11), dodecenoic acid (C12), tridecenoic acid (C13), tetradecenoic acid (C14),
pentadecenoic acid (C15), hexadecenoic acid (C16), heptadecenoic acid (C17), octadecenoic
acid (C18), nonadecenoic acid (C19), icosenoic acid (C20), henicosenoic acid (C21),
docosenoic acid (C22), tricosenoic acid (C23), tetracosenoic acid (C24), pentacosenoic
acid (C25), hexacosenoic acid (C26), heptacosenoic acid (C27), octacosenoic acid (C28),
nonacosenoic acid (C29), triacontenoic acid (C30).
[0072] Specific examples of the fatty acid (Common name) are, formic acid (C1), acetic acid
(C2), propionic acid (C3), butyric acid (C4), valeric acid (C5), caproic acid (C6),
enanthic acid (C7), caprylic acid (C8), pelargonic acid (C9), capric acid (C10), lauric
acid (C12), myristic acid (C14), myristoleic acid (C14), pentadecylic acid (C15),
palmitic acid (C16), palmitoleic acid (C16), margaric acid (C17), stearic acid (C18),
elaidic acid (C18), vaccenic acid (C18), oleic acid (C18), linoleic acid (C18), linolenic
acid (C18), 12-hydroxystearic acid (C18), arachidic acid (C20), gadoleic acid (C20),
arachidonic acid (C20), eicosenoic acid (C20), behenic acid (C22), erucic acid (C22),
lignoceric acid (C24), nervonic acid (C24), cerotic acid (C26), montanic acid (C28),
and melissic acid (C30). The fatty acid may be used alone or as a mixture of at least
two of them. Among those described above, capric acid, lauric acid, myristic acid,
palmitic acid, setaric acid, behenic acid and oleic acid are preferable as the fatty
acid.
[0073] There is no particular limitation on the aromatic carboxylic acid, as long as it
is a compound that has an aromatic ring and a carboxyl group. Specific examples of
the aromatic carboxylic acid include, for example, benzoic acid (C7), phthalic acid
(C8), isophthalic acid (C8), terephthalic acid (C8), hemimellitic acid (benzene-1,2,3-tricarboxylic
acid) (C9), trimellitic acid (benzene-1,2,4-tricarboxylic acid) (C9), trimesic acid
(benzene-1,3,5-tricarboxylic acid) (C9), mellophanic acid (benzene-1,2,3,4-tetracarboxylic
acid) (C10), prehnitic acid (benzene-1,2,3,5-tetracarboxylic acid) (C10), pyromellitic
acid (benzene-1,2,4,5-tetracarboxylic acid) (C10), mellitic acid (benzene hexacarboxylic
acid) (C12), diphenic acid (biphenyl-2,2'-dicarboxylic acid) (C12), toluic acid (methylbenzoic
acid) (C8), xylic acid (C9), prehnitylic acid (2,3,4-trimethylbenzoic acid) (C10),
γ-isodurylic acid (2,3,5-trimethylbenzoic acid) (C10), durylic acid (2,4,5-trimethylbenzoic
acid) (C10), β-isodurylic acid (2,4,6-trimethylbenzoic acid) (C10), α-isodurylic acid
(3,4,5-trimethylbenzoic acid) (C10), cuminic acid (4-isopropylbenzoic acid) (C10),
uvitic acid (5-methylisophthalic acid) (C9), α-toluic acid (phenylacetic acid) (C8),
hydratropic acid (2-phenylpropanoic acid) (C9), and hydrocinnamic acid (3-phenylpropanoic
acid) (C9).
[0074] Furthermore, examples of the aromatic carboxylic acid substituted with a hydroxyl
group, an alkoxy group, or an oxo group include salicylic acid (2-hydroxybenzoic acid)
(C7), anisic acid (methoxybenzoic acid) (C8), cresotinic acid (hydroxy (methyl) benzoic
acid) (C8), o-homosalicylic acid (2-hydroxy-3-methylbenzoic acid) (C8), m-homosalicylic
acid (2-hydroxy-4-methylbenzoic acid) (C8), p-homosalicylic acid (2-hydroxy-5-methylbenzoic
acid) (C8), o-pyrocatechuic acid (2,3-dihydroxybenzoic acid) (C7), β-resorcylic acid
(2,4-dihydroxybenzoic acid) (C7), γ-resorcylic acid (2,6-dihydroxybenzoic acid) (C7),
protocatechuic acid (3,4-dihydroxybenzoic acid) (C7), α-resorcylic acid (3,5-dihydroxybenzoic
acid) (C7), vanillic acid (4-hydroxy-3-methoxybenzoic acid) (C8), isovanillic acid
(3-hydroxy-4-methoxybenzoic acid) (C8), veratric acid (3,4-dimethoxybenzoic acid)
(C9), o-veratric acid (2,3-dimethoxybenzoic acid) (C9), orsellinic acid (2,4-dihydroxy-6-methylbenzoic
acid) (C8), m-hemipinic acid (4,5-dimethoxyphthalic acid) (C10), gallic acid (3,4,5-trihydroxybenzoic
acid) (C7), syringic acid (4-hydroxy-3,5-dimethoxybenzoic acid) (C9), asaronic acid
(2,4,5-trimethoxybenzoic acid) (C10), mandelic acid (hydroxy (phenyl) acetic acid)
(C8), vanilmandelic acid (hydroxy (4-hydroxy-3-methoxy phenyl) acetic acid) (C9),
homoanisic acid ((4-methoxy phenyl) acetic acid) (C9), homogentisic acid ((2,5-dihydroxyphenyl)
acetic acid) (C8), homoprotocatechuic acid ((3,4-dihydroxyphenyl) acetic acid) (C8),
homovanillic acid ((4-hydroxy-3-methoxy phenyl) acetic acid) (C9), homoisovanillic
acid ((3-hydroxy-4-methoxy phenyl) acetic acid) (C9), homoveratric acid ((3,4-dimethoxy
phenyl) acetic acid) (C10), o-homoveratric acid ((2,3-dimethoxy phenyl) acetic acid)
(C10), homophthalic acid (2-(carboxymethyl) benzoic acid) (C9), homoisophthalic acid
(3-(carboxymethyl) benzoic acid) (C9), homoterephthalic acid (4-(carboxymethyl) benzoic
acid) (C9), phthalonic acid (2-(carboxycarbonyl) benzoic acid) (C9), isophthalonic
acid (3-(carboxycarbonyl) benzoic acid) (C9), terephthalonic acid (4-(carboxycarbonyl)
benzoic acid) (C9), benzilic acid (hydroxy diphenylacetic acid) (C14), atrolactic
acid (2-hydroxy-2-phenylpropanoic acid) (C9), tropic acid (3-hydroxy-2-phenylpropanoic
acid) (C9), melilotic acid (3-(2-hydroxyphenyl) propanoic acid) (C9), phloretic acid
(3-(4-hydroxy phenyl) propanoic acid) (C9), hydrocaffeic acid (3-(3,4-dihydroxyphenyl)
propanoic acid) (C9), hydroferulic acid (3-(4-hydroxy-3-methoxy phenyl) propanoic
acid) (C10), hydroisoferulic acid (3-(3-hydroxy-4-methoxy phenyl) propanoic acid)
(C10), p-coumaric acid (3-(4-hydroxy phenyl) acrylic acid) (C9), umbellic acid (3-(2,4-dihydroxyphenyl)
acrylic acid) (C9), caffeic acid (3-(3,4-dihydroxyphenyl) acrylic acid) (C9), ferulic
acid (3-(4-hydroxy-3-methoxy phenyl) acrylic acid) (C10), isoferulic acid (3-(3-hydroxy-4-methoxy
phenyl) acrylic acid) (C10), and sinapic acid (3-(4-hydroxy-3,5-dimethoxy phenyl)
acrylic acid) (C11).
[0075] The cation component of (d) the salt of the acid may be any one of a metal ion, an
ammonium ion and an organic cation. The metal ion includes monovalent metal ions such
as sodium, potassium, lithium, silver and the like; divalent metal ions such as magnesium,
calcium, zinc, barium, cadmium, copper, cobalt, nickel, manganese and the like; trivalent
metal ions such as aluminum, iron and the like; and other ions such as tin, zirconium,
titanium and the like. As the cation component of the salt of the carboxylic acid,
a zinc ion is preferable. The cation components may be used alone or as a mixture
of at least two of them.
[0076] The organic cation includes a cation having a carbon chain. The organic cation includes,
for example, without limitation, an organic ammonium ion. Examples of the organic
ammonium ion are: primary ammonium ions such as stearyl ammonium ion, hexyl ammonium
ion, octyl ammonium ion, 2-ethyl hexyl ammonium ion or the like; secondary ammonium
ions such as dodecyl (lauryl) ammonium ion, octadecyl (stearyl) ammonium ion or the
like; tertiary ammonium ions such as trioctyl ammonium ion or the like; and quaternary
ammonium ions such as dioctyldimethyl ammonium ion, distearyldimethyl ammonium ion
or the like. Those organic cation may be used alone or as a mixture of at least two
of them.
[0077] The content of (d) the acid and/or the salt thereof is preferably 1.0 part by mass
or more, more preferably 1.5 parts by mass or more, even more preferably 2.0 parts
by mass or more, and is preferably less than 40 parts by mass, more preferably 30
parts by mass or less, even more preferably 20 parts by mass or less. If the content
is too little, the effect of adding (d) the acid and/or the salt thereof is not sufficient,
and thus the degree of the outer-hard inner-soft of the outer core layer may be small.
If the content is too much, the resilience of the core may be lowered, since the hardness
of the resultant outer core layer may be lowered as a whole.
[0078] There are cases where the surface of the zinc acrylate used as the co-crosslinking
agent is treated with (d) the acid and/or the salt thereof to improve the dispersibility
to the rubber. In the case of using zinc acrylate whose surface is treated with (d)
the acid and/or the salt thereof, in the present invention, the amount of (d) the
acid and/or the salt thereof used as a surface treating agent is not included in the
content of (d) component. It is not conceivable that the (d) the acid and/or the salt
thereof hardly contribute to the cation exchange reaction with (b) the co-crosslinking
agent.
[0079] The content of (d) the acid and/or the salt thereof is preferably determined by the
kind and the combination of the acid and/or the salt thereof to be used. Particularly,
the content of (d) the acid and/or the salt thereof is preferably determined by the
carbon number and the combination of the acid and/or the salt thereof. It is conceivable
that the action of breaking the metal crosslinking is affected by the number of moles
of the acid and/or the salt thereof to be added. Concurrently, the acid and/or the
salt thereof acts as a plasticizer for the outer core layer. If the blending amount
(mass) of the acid and/or the salt thereof to be added increases, the entire outer
core layer is softened. This plasticizing effect is affected by the blending amount
(mass) of the acid and/or the salt thereof to be added. In view of those actions,
on the same blending amount (mass), the number of moles of the acid and/or the salt
thereof to be added is made larger by using the acid and/or the salt thereof having
less carbon atoms (small molecular weight) compared to using the acid and/or the salt
thereof having larger carbon atoms (large molecular weight). That is, the acid and/or
the salt thereof having less carbon atoms can enhance the effect of breaking the metal
crosslinking, while suppressing softening the entire outer core layer by the plasticizing
effect.
[0080] For example, if a carboxylic acid having 1 to 14 carbon atoms and/or a salt thereof
is used as (d) the acid and/or the salt thereof, the content of the carboxylic acid
having 1 to 14 carbon atoms and/or a salt thereof is preferably 1.0 part by mass or
more, more preferably 1.2 parts by mass or more, even more preferably 1.4 parts by
mass or more, and is preferably 20 parts by mass or less, more preferably 18 parts
by mass or less, even more preferably 16 parts by mass or less with respect to 100
parts by mass of (a) the base rubber. The carbon number of the salt of the carboxylic
acid having 1 to 14 carbon atoms is the carbon number of the carboxylic acid component,
and the carbon number of the organic cation is not included.
[0081] For example, if a carboxylic acid having 15 to 30 carbon atoms and/or a salt thereof
is used as (d) the acid and/or the salt thereof, the content of the carboxylic acid
having 15 to 30 carbon atoms and/or the salt thereof is preferably 5 parts by mass
or more, more preferably 6 parts by mass or more, even more preferably 7 parts by
mass or more, and is preferably less than 40 parts by mass, more preferably 35 parts
by mass or less, even more preferably 30 parts by mass or less with respect to 100
parts by mass of (a) the base rubber. The carbon number of the salt of the carboxylic
acid having 15 to 30 carbon atoms is the carbon number of the carboxylic acid component,
and the carbon number of the organic cation is not included.
[0082] If a carboxylic acid having 15 to 30 carbon atoms and/or a salt thereof is used as
(d) the acid and/or the salt thereof, the content of the carboxylic acid having 15
to 30 carbon atoms and/or the salt thereof is preferably 10 parts by mass or more,
more preferably 15 parts by mass or more, even more preferably 20 parts by mass or
more, and is preferably less than 70 parts by mass, more preferably 60 parts by mass
or less, even more preferably 50 parts by mass or less with respect to 100 parts by
mass of (b) the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms and/or
the metal salt thereof.
[0083] The rubber composition used in the present invention preferably further contains
(e) an organic sulfur compound. By using (e) the organic sulfur compound and (d) the
acid and/or the salt thereof in combination for the rubber composition, the degree
of the outer-hard and inner-soft structure of the outer core layer can be controlled,
while maintaining approximate linearity of the hardness distribution of the outer
core layer.
[0084] (e) The organic sulfur compound is not particularly limited, as long as it is an
organic compound having a sulfur atom in the molecule thereof. Examples thereof include
an organic compound having a thiol group (-SH), a polysulfide bond having 2 to 4 sulfur
atoms (-S-S-, -S-S-S-, or -S-S-S-S-), or a metal salt thereof (-SM, -S-M-S-, -S-M-S-S-,
-S-S-M-S-S-, -S-M-S-S-S-, or the like; M is a metal atom). Furthermore, (e) the organic
sulfur compound may be any one of aliphatic compounds (aliphatic thiol, aliphatic
thiocarboxylic acid, aliphatic dithiocarboxylic acid, aliphatic polysulfides, or the
like), heterocyclic compounds, alicyclic compounds (alicyclic thiol, alicyclic thiocarboxylic
acid, alicyclic dithiocarboxylic acid, alicyclic polysulfides, or the like), and aromatic
compounds.
(e) The organic sulfur compound includes, for example, thiophenols, thionaphthols,
polysulfides, thiocarboxylic acids, dithiocarboxylic acids, sulfenamides, thiurams,
thiuramdisulfides, dithiocarbamates, and thiazoles. From the aspect of the larger
hardness distribution of the spherical core, (e) the organic sulfur compound preferably
includes, organic compounds having a thiol group (-SH) or a metal salt thereof, more
preferably thiophenols, thionaphthols, or a metal salt thereof. Examples of the metal
salts are salts of monovalent metals such as sodium, lithium, potassium, copper (I),
and silver (I), and salts of divalent metals such as zinc, magnesium, calcium, strontium,
barium, titanium (II), manganese (II), iron (II), cobalt (II), nickel(II), zirconium(II),
and tin (II).
[0085] Examples of the thiophenols include thiophenol; thiophenols substituted with a fluoro
group such as 4-fluorothiophenol, 2,5-difluorothiophenol, 2,4,5-trifluorothiophenol,
2,4,5,6-tetrafluorothiophenol, pentafluorothiophenol; thiophenols substituted with
a chloro group such as 2-chlorothiophenol, 4-chlorothiophenol, 2,4-dichlorothiophenol,
2,5-dichlorothiophenol, 2,6-dichlorothiophenol, 2,4,5-trichlorothiophenol, 2,4,5,6-tetrachlorothiophenol,
pentachlorothiophenol; thiophenols substituted with a bromo group such as 4-bromothiophenol,
2,5-dibromothiophenol, 2,4,5-tribromothiophenol, 2,4,5,6-tetrabromothiophenol, pentabromothiophenol;
thiophenols substituted with a iodo group such as 4-iodothiophenol, 2,5-diiodothiophenol,
2,4,5-triiodothiophenol, 2,4,5,6-tetraiodothiophenol, pentaiodothiophenol; or a metal
salt thereof. The metal salt is preferably zinc salt.
[0086] Examples of the thionaphthols (naphthalenethiols) are 2-thionaphthol, 1-thionaphthol,
2-chloro-1-thionaphthol, 2-bromo-1-thionaphthol, 2-fluoro-1-thionaphthol, 2-cyano-1-thionaphthol,
2-acetyl-1-thionaphthol, 1-chloro-2-thionaphthol, 1-bromo-2-thionaphthol, 1-fluoro-2-thionaphthol,
1-cyano-2-thionaphthol, and 1-acetyl-2-thionaphthol and metal salts thereof. Preferable
examples include 1-thionaphthol, 2-thionaphthol and zinc salt thereof.
[0087] The sulfenamide based organic sulfur compound includes, for example, N-cyclohexyl-2-benzothiazole
sulfenamide, N-oxydiethylene-2-benzothiazole sulfenamide, and N-t-butyl-2-benzothiazole
sulfenamide. The thiuram based organic sulfur compound includes, for example, tetramethylthiuram
monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram
disulfide, and dipentamethylenethiuram tetrasulfide. The dithiocarbamates include,
for example, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, zinc dibutyldithiocarbamate,
zinc ethylphenyl dithiocarbamate, sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate,
copper (II) dimethyldithiocarbate, iron (III) dimethyldithiocarbamate, selenium diethyldithiocarbamate,
and tellurium diethyldithiocarbamate. The thiazole based organic sulfur compound includes,
for example, 2-mercaptobenzothiazole (MBT), dibenzothiazyl disulfide (MBTS), sodium
salt, zinc salt, copper salt, or cyclohexylamine salt of 2-mercaptobenzothiazole,
2-(2,4-dinitrophenyl) mercaptobenzothiazole, and 2-(2,6-diethyl-4-morpholinothio)
benzothiazole. (e) The organic sulfur compounds may be used alone or as a mixture
of at least two of them.
[0088] The content of (e) the organic sulfur compound is preferably 0.05 part by mass or
more, more preferably 0.1 part by mass or more, and is preferably 5.0 parts by mass
or less, more preferably 2.0 parts by mass or less, with respect to 100 parts by mass
of (a) the base rubber. If the content of (e) the organic sulfur compound is less
than 0.05 part by mass, the effect of adding (e) the organic sulfur compound cannot
be obtained and thus the resilience may not improve. If the content of (e) the organic
sulfur compound exceeds 5.0 parts by mass, the compression deformation amount of the
obtained golf ball becomes large and thus the resilience may be lowered.
[0089] The rubber composition used in the present invention can include additives such as
a pigment, a filler for adjusting weight or the like, an antioxidant, a peptizing
agent, and a softener where necessary. Further, as described above, if the rubber
composition used in the present invention contains only (b1) the α,β-unsaturated carboxylic
acid having 3 to 8 carbon atoms as a co-crosslinking agent, the rubber composition
preferably contains (f) the metal compound.
(f) The metal compound is not limited, as long as it can neutralize (b1) the α,β-unsaturated
carboxylic acid having 3 to 8 carbon atoms in the rubber composition. Examples of
(f) the metal compounds are metal hydroxides such as magnesium hydroxide, zinc hydroxide,
calcium hydroxide, sodium hydroxide, lithium hydroxide, potassium hydroxide, copper
hydroxide, and the like; metal oxides such as magnesium oxide, calcium oxide, zinc
oxide, copper oxide, and the like; metal carbonates such as magnesium carbonate, zinc
carbonate, calcium carbonate, sodium carbonate, lithium carbonate, potassium carbonate,
and the like. From the aspect of reacting with (b1) the α,β-unsaturated carboxylic
acid having 3 to 8 carbon atoms as the co-crosslinking agent to form a metal crosslinking,
(f) the metal compound preferably includes a divalent metal compound, more preferably
includes a zinc compound. Use of the zinc compound provides a golf ball with excellent
resilience. (f) The metal compound may be used alone or as a mixture of at least two
of them. The content of (f) the metal compound is preferably determined in accordance
with the desired degree of neutralization of the carboxyl group of (b) the α,β-unsaturated
carboxylic acid having 3 to 8 carbon atoms.
[0090] Examples of the pigment blended in the rubber composition include a white pigment,
a blue pigment, and a purple pigment. As the white pigment, titanium oxide is preferably
used. The type of titanium oxide is not particularly limited, but rutile type is preferably
used because of the high opacity. The blending amount of titanium oxide is preferably
0.5 part by mass or more, and more preferably 2 parts by mass or more, and is preferably
8 parts by mass or less, and more preferably 5 parts by mass or less, with respect
to 100 parts by mass of (a) the base rubber.
[0091] It is also preferred that the rubber composition contains both a white pigment and
a blue pigment. The blue pigment is blended in order to cause white color to be vivid,
and examples thereof include ultramarine blue, cobalt blue, and phthalocyanine blue.
Examples of the purple pigment include anthraquinone violet, dioxazine violet, and
methyl violet.
[0092] The blending amount of the blue pigment is preferably 0.001 part by mass or more,
and more preferably 0.05 part by mass or more, and is preferably 0.2 part by mass
or less, and more preferably 0.1 part by mass or less, with respect to 100 parts by
mass of (a) the base rubber. If the blending amount of the blue pigment is less than
0.001 part by mass, blueness is insufficient, and the color looks yellowish. If the
blending amount of the blue pigment exceeds 0.2 part by mass, blueness is excessively
strong, and a vivid white appearance is not provided.
[0093] The filler blended in the rubber composition is used as a weight adjusting agent
for mainly adjusting the weight of the golf ball obtained as an final product. The
filler may be blended where necessary. The filler includes, for example, inorganic
fillers such as zinc oxide, barium sulfate, calcium carbonate, magnesium oxide, tungsten
powder, molybdenum powder, or the like. The filler more preferably includes zinc oxide.
It is considered that zinc oxide functions as a vulcanization aid to enhance the hardness
of the whole core. The content of the filler is preferably 0.5 part by mass or more,
more preferably 1 part by mass or more, and is preferably 30 parts by mass or less,
more preferably 25 parts by mass or less, even more preferably 20 parts by mass or
less. If the content of the filler is less than 0.5 part by mass, it is difficult
to adjust the weight, while if the content of the filler exceeds 30 parts by mass,
the weight ratio of the rubber component becomes small and thus the resilience tends
to be lowered.
[0094] The blending amount of the antioxidant is preferably 0.1 part by mass or more and
1 part by mass or less, with respect to 100 parts by mass of (a) the base rubber.
In addition, the blending amount of the peptizing agent is preferably 0.1 part by
mass or more and 5 parts by mass or less, with respect to 100 parts by mass of (a)
the base rubber.
(3) Inner Core Layer Composition
[0095] Material for the inner core layer includes a rubber composition or a resin composition.
As the inner core layer rubber composition, exemplified is a rubber composition containing,
for example, (a) a base rubber, (b) a co-crosslinking agent, and (c) a crosslinking
initiator. As (a) the base rubber, (b) the co-crosslinking agent, and (c) the crosslinking
initiator, the same components used for the outer core layer rubber composition can
be used.
[0096] In the inner core layer rubber composition, (f) an organic sulfur compound, (e) a
metal compound, a filler, an antioxidant, and a peptizing agent may be blended appropriately
in addition to (a) the base rubber, (b) the co-crosslinking agent, and (c) the crosslinking
initiator. With regard to these components, the same components used in the outer
core layer composition can be used. It is preferred that (d) the acid and/or the salt
thereof is not blended in the inner core layer rubber composition. However, in the
case that (d) the acid and/or the salt thereof is blended in the inner core layer
rubber composition, the content thereof is preferably more than 40 parts by mass with
respect to 100 parts by mass of (a) the base rubber.
[0097] The resin component includes a binary copolymer composed of an olefin and an α,β-unsaturated
carboxylic acid having 3 to 8 carbon atoms, a ternary copolymer composed of an olefin,
an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms, and an α,β-unsaturated
carboxylic acid ester, a binary ionomer resin consisting of a metal ion neutralized
product of a binary copolymer composed of an olefin and an α,β-unsaturated carboxylic
acid having 3 to 8 carbon atoms, and a ternary ionomer resin consisting of a metal
ion-neutralized product of a ternary copolymer composed of an olefin, an α,β-unsaturated
carboxylic acid having 3 to 8 carbon atoms, and an α,β-unsaturated carboxylic acid
ester.
[0098] Specific examples of the binary copolymer include an ethylene-methacrylic acid copolymer
such as "NUCREL (registered trademark) (e.g. NUCREL N1050H, NUCREL N2050H, NUCREL
N1110H, NUCREL N0200H) manufactured by Du Pont-Mitsui Polychemicals Co., Ltd. Specific
examples of the ternary copolymer include "NUCREL (registered trademark) (e.g. NUCREL
AN4318, NUCREL AN4319) manufactured by Du Pont-Mitsui Polychemicals Co., Ltd.
[0099] Specific examples of the binary ionomer resin include trade name "Himilan (registered
trademark) (e.g. Himilan 1555 (Na), Himilan 1557 (Zn), Himilan 1605 (Na), Himilan
1706 (Zn), Himilan 1707 (Na), Himilan AM7311 (Mg), Himilan AM7329 (Zn))" commercially
available from Du Pont-Mitsui Polychemicals Co., Ltd. Specific examples of the ternary
ionomer resin include trade name "Himilan (registered trademark) (e.g. Himilan AM7327
(Zn), Himilan 1855 (Zn), Himilan 1856 (Na), Himilan AM7331 (Na), or the like)" commercially
available from Du Pont-Mitsui Polychemicals Co., Ltd. When the binary copolymer or
ternary copolymer is used as the resin component, a metal compound may be blended.
The metal compound includes (e) the metal compound used for the outer core layer rubber
composition.
[0100] When the resin composition is used for the inner core layer, an amphoteric surfactant
having a cationic part and anionic part may be blended. Examples of the amphoteric
surfactant include a betaine type amphoteric surfactant such as alkylbetaine type,
amidobetaine type, imidazoliumbetaine type, alkylsulfobetain type, amidosulfobetain
type, and the like; amidoamino acid type amphoteric surfactant and alkylamino fatty
acid salt; alkylamine oxide; β-alanine type amphoteric surfactant and glycine type
amphoteric surfactant; sulfobetaine type amphoteric surfactant; phosphobetaine type
amphoteric surfactant; and the like.
[0101] Specific examples of the amphoteric surfactant are dimethyllaurylbetaine, oleyldimethylaminoacetic
acid betaine (oleylbetaine), dimethyloleylbetaine, dimethylstearylbetaine, stearyldihydroxymethylbetaine,
stearyldihydroxyethylbetaine, lauryldihydroxymethylbetaine, lauryldihydroxyethylbetaine,
myristyldihydroxymethylbetaine, behenyldihydroxymethylbetaine, palmityldihydroxyethylbetaine,
oleyldihydroxymethylbetaine, coconut oil fatty acid amidopropylbetaine, lauric acid
amidoalkylbetaine, 2-alkyl-N-carboxyalkylimidazoliumbetaine, lauric acid amidoalkylhydroxysulfobetaine,
coconut oil fatty acid amidodialkylhydroxyalkylsulfobetaine, N-alkyl-β-aminopropionic
acid salt, N-alkyl-β-iminodipropionic acid salt, alkyldiaminoalkylglycine, alkylpolyaminoalkylglycine,
sodium salt of alkylamino fatty acid, N,N-dimethyloctylamine oxide, N,N-dimethyllaurylamine
oxide, N,N-dimethylstearylamine oxide, and the like.
[0102] The content of the amphoteric surfactant is preferably 10 parts by mass or more,
more preferably 15 parts by mass or more, even more preferably 20 parts by mass or
more, and is preferably 100 parts by mass or less, more preferably 90 parts by mass
or less, even more preferably 80 parts by mass or less with respect to 100 parts by
mass of the base resin.
[0103] If the inner core layer includes the resin composition, a basic metal salt of a fatty
acid may be blended. By blending the basic metal salt of the fatty acid, the resilience
performance is improved. The basic metal salt of the fatty acid is preferably a basic
metal salt of a saturated fatty acid. The basic metal salt of the fatty acid is preferably
a basic metal salt of a fatty acid having 4 to 22 carbon atoms, and more preferably
basic metal salt of a fatty acid having 5 to 18 carbon atoms. Specific examples of
the basic metal salt of the fatty acid include basic magnesium caprylate, basic calcium
caprylate, basic zinc caprylate, basic magnesium laurate, basic calcium laurate, basic
zinc laurate, basic magnesium myristate, basic calcium myristate, basic zinc myristate,
basic magnesium palmitate, basic calcium palmitate, basic zinc palmitate, basic magnesium
oleate, basic calcium oleate, basic zinc oleate, basic magnesium stearate, basic calcium
stearate, basic zinc stearate, basic magnesium 12-hydroxystearate, basic calcium 12-hydroxystearate,
basic zinc 12-hydroxystearate, basic magnesium behenate, basic calcium behenate, and
basic zinc behenate. The basic metal salt of the fatty acid preferably includes basic
zinc fatty acid, and more preferably basic zinc stearate, basic zinc laurate, and
basic zinc caprylate. The basic metal salt of the fatty acid may be used alone or
as a mixture of at least two of them.
[0104] The content of the basic metal salt of the fatty acid is preferably 3 parts by mass
or more, more preferably 5 parts by mass or more, even more preferably 10 parts by
mass or more, and is preferably 80 parts by mass or less, more preferably 60 parts
by mass or less, even more preferably 50 parts by mass or less with respect 100 parts
by mass of the base resin.
(4) Intermediate Layer Composition
[0105] An intermediate layer composition containing a resin component is preferably used
for the intermediate layer. Examples of the resin component include ionomer resins,
styrene block-containing thermoplastic elastomers, thermoplastic polyurethane elastomers,
thermoplastic polyamide elastomers, thermoplastic polyester elastomers, thermoplastic
polyolefin elastomers, and thermoplastic styrene elastomers. Among these, ionomer
resins are preferred as the resin component. Ionomer resins are highly elastic.
[0106] An ionomer resin and another resin may be used in combination. In this case, from
the aspect of the resilience performance, the ionomer resin is the principal component
of the resin component. The content of the ionomer resin in the resin component is
preferably 50 mass % or more, more preferably 70 mass % or more, and even more preferably
85 mass % or more.
[0107] Examples of the ionomer resin include, for example, one prepared by neutralizing
at least a part of carboxyl croups in a binary copolymer composed of an olefin and
an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms with a metal ion, one
prepared by neutralizing at least a part of carboxyl groups in a ternary copolymer
composed of an olefin, an α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms
and an α,β-unsaturated carboxylic acid ester, or a mixture of them. The olefin preferably
includes an olefin having 2 to 8 carbon atoms. Examples of the olefin include ethylene,
propylene, butene, pentene, hexene, heptene and octene. Among them, ethylene is more
preferred. Examples of the α,β-unsaturated carboxylic acid having 3 to 8 carbon atoms
are acrylic acid, methacrylic acid, fumaric acid, maleic acid and crotonic acid. Among
these, acrylic acid or methacrylic acid is particularly preferred. Examples of the
α,β-unsaturated carboxylic acid ester are methyl, ethyl, propyl, n-butyl, isobutyl
ester and the like of acrylic acid, methacrylic acid, fumaric acid and maleic acid.
Particularly, acrylic acid ester and methacrylic acid ester are preferred. Among them,
as the ionomer resin, preferred are a metal ion-neutralized product of the binary
copolymer composed of ethylene-(meth)acrylic acid and a metal ion-neutralized product
of the ternary copolymer composed of ethylene-(meth)acrylic acid-(meth)acrylic acid
ester.
[0108] Specific examples of the ionomer resin include trade name "Himilan (registered trademark)
(e.g. Himilan 1555 (Na), Himilan 1557 (Zn), Himilan 1605 (Na), Himilan 1706 (Zn),
Himilan 1707 (Na), Himilan AM3711 (Mg))", and specific examples of the ternary ionomer
resin include "Himilan 1856 (Na), Himilan 1855 (Zn), Himilan AM7329 (Zn)" commercially
available from Du Pont-Mitsui Polychemicals Co., Ltd.
[0109] Further, examples include "Surlyn (registered trademark) (e.g. the binary copolymerized
ionomer such as Surlyn 8945 (Na), Surlyn 9945 (Zn), Surlyn 8140 (Na), Surlyn 8150
(Na), Surlyn 9120 (Zn), Surlyn 9150 (Zn), Surlyn 6910 (Mg), Surlyn 6120 (Mg), Surlyn
7930 (Li), Surlyn 7940 (Li), Surlyn AD8546 (Li); and the ternary copolymerized ionomer
such as Surlyn 8120 (Na), Surlyn 8320 (Na), Surlyn 9320 (Zn), Surlyn 6320 (Mg), HPF
1000 (Mg), HPF 2000 (Mg))" commercially available from E.I. du Pont de Nemours and
Company.
[0110] Further, examples include "lotek (registered trademark) (e.g. the binary copolymerized
ionomer such as lotek 8000 (Na), lotek 8030 (Na), lotek 7010 (Zn), lotek 7030 (Zn);
and the ternary copolymerized ionomer such as lotek 7510 (Zn), lotek 7520 (Zn))" commercially
available from ExxonMobil Chemical Corporation.
[0111] It is noted that Na, Zn, Li, and Mg described in the parentheses after the trade
names indicate metal types of neutralizing metal ions for the ionomer resins. The
above ionomer resins may be used solely or as a mixture of two or more of them.
[0112] Examples of the thermoplastic styrene elastomers include "Rabalon (registered trademark)"
commercially available from Mitsubishi Chemical Corporation.
[0113] The intermediate layer composition may further contain a pigment component such as
a white pigment (for example, titanium oxide), a blue pigment, and a red pigment;
a weight adjusting agent such as zinc oxide, calcium carbonate, and barium sulfate;
a dispersant; an antioxidant; an ultraviolet absorber; a light stabilizer; a fluorescent
material or a fluorescent brightener; and the like, as long as they do not impair
the effect of the present invention.
(5) Reinforcing Layer Composition
[0114] The reinforcing layer adheres firmly to the intermediate layer as well as to the
cover. The reinforcing layer suppresses delamination of the cover from the intermediate
layer. The reinforcing layer is preferably formed between the intermediate layer and
the cover, especially in the case that the intermediate layer is formed from an intermediate
layer composition containing a base resin and the cover composition containing a base
resin, and that the base resins contained in the intermediate layer and the cover
are different each other (for example, the intermediate layer composition contains
an ionomer resin as the base resin and the cover composition contains the thermoplastic
polyurethane as the base resin).
[0115] The reinforcing layer is formed from a reinforcing layer composition containing a
resin component. As the resin component, a two-component curing type thermosetting
resin is preferably used. Example of two-component curing type thermosetting resin
include epoxy resins, urethane resins, acrylic resins, polyester resins and cellulose
resins. From the aspect of the strength and durability of the reinforcing layer, two-component
curing type epoxy resins and two-component curing type urethane resins are preferred.
[0116] The reinforcing layer composition may include additives such as a coloring agent
(for example, titanium dioxide), a phosphoric acid-based stabilizer, an antioxidant,
a light stabilizer, a fluorescent brightener, an ultraviolet absorber, an anti-blocking
agent and the like. The additives may be added to either the base material or the
curing agent of the two-component curing thermosetting resin.
(6) Cover Composition
[0117] The cover of the golf ball of the present invention is formed from a cover composition
containing a resin component. Examples of the resin components include an ionomer
resin, a thermoplastic polyamide elastomer having a trade name "Pebax (registered
trademark) (e.g. "Pebax 2533")" commercially available from Arkema Inc., a thermoplastic
polyester elastomer having a trade name "Hytrel (registered trademark) (e.g. "Hytrel
3548" and "Hytrel 4047")" commercially available from Du Pont-Toray Co., Ltd., a thermoplastic
polyurethane elastomer having a trade name "Elastollan (registered trademark)" commercially
available from BASF Japan Ltd., a thermoplastic styrene elastomer having a trade name
"Rabalon (registered trademark)" commercially available from Mitsubishi Chemical Corporation,
and the like. These resin components may be used alone or in combination of two or
more thereof.
[0118] The cover composition constituting the cover of the golf ball of the present invention
preferably contains the thermoplastic polyurethane as a resin component. The content
of the thermoplastic polyurethane in the resin component of the cover composition
is preferably 50 mass % or more, more preferably 60 mass % or more, even more preferably
70 mass % or more.
[0119] The cover composition may contain a pigment component such as a white pigment (for
example, titanium oxide), a blue pigment, a red pigment, or the like, a specific gravity
adjusting agent such as zinc oxide, calcium carbonate, barium sulfate, or the like,
a dispersant, an antioxidant, an ultraviolet absorber, a light stabilizer, a fluorescent
material or a fluorescent brightener, or the like as long as they do not impair the
performance of the cover.
[0120] The amount of the white pigment (for example, titanium oxide) is preferably 0.5 part
or more, more preferably 1 part or more, and the content of the white pigment is preferably
10 parts or less, more preferably 8 parts or less, with respect to 100 parts of the
resin component constituting the cover by mass. If the amount of the white pigment
is 0.5 part by mass or more, it is possible to impart the opacity to the resultant
cover. Further, if the amount of the white pigment is more than 10 parts by mass,
the durability of the resultant cover may deteriorate.
(7) Method for Manufacturing Golf Ball
[0121] The inner core layer used in the present invention is prepared using the rubber composition
or the resin composition for the inner core layer. If the inner core layer is formed
from the rubber composition, the inner core layer is obtained by heating and molding
the kneaded rubber composition in the molds. The temperature for press-molding into
the inner core layer is preferably 140°C or more, more preferably 145°C or more, even
more preferably 150°C or more, and is preferably 160°C or less. The pressure for press-molding
preferably ranges from 5 MPa to 30 MPa. The time for press-molding is preferably from
10 minutes to 40 minutes.
[0122] If the inner core layer is formed from the resin composition, the inner core layer
is molded by injection molding. The molding by the injection molding method is conducted
by charging and cooling the resin composition. For example, the resin composition
heated and melted at the temperature ranging from 160°C to 260°C is charged into molds
clamped under the pressure of 1 MPa to 100 MPa for 1 second to 100 seconds, and after
cooling for 30 seconds to 300 seconds, the molds are opened.
[0123] A method for molding the outer core layer includes, for example, an embodiment which
comprises molding the outer core layer composition into a hollow-shell, covering the
inner core layer with a plurality of the hollow-shells and subjecting the inner core
layer with a plurality of the hollow shells to the compression-molding (preferably
an embodiment which comprises molding the rubber composition into a half hollow-shell,
covering the inner core layer with the two half hollow-shells, and subjecting the
inner core layer with the two half hollow-shells to the compression-molding). The
compression-molding of the rubber composition into a half shell can be carried out,
for example, under a pressure of 1 MPa or more and 100 MPa or less at a molding temperature
of 10°C or more and 60°C or less. A method for molding the outer core layer using
the half shells includes, for example, compression molding the inner core layer covered
with the two half shells. The compression molding of half shells into the outer core
layer can be carried out, for example, under a pressure of 1 MPa or more and 100 MPa
or less at a molding temperature of 140°C or more and 180°C or less. By performing
the molding under the above conditions, the outer core layer having a uniform thickness
can be formed.
[0124] The rubber composition used in the present invention is obtained by mixing and kneading
(a) the base rubber, (b) the α,β-unsaturated carboxylic acid having 3 to 8 carbon
atoms and/or the metal salt thereof, (c) the crosslinking initiator, and (d) the acid
and/or the salt thereof, if necessary other additives. The kneading can be conducted,
without any limitation, with a publicly known kneading machine such as a kneading
roll, a banbury mixer, a kneader, or the like.
[0125] A method for molding an intermediate layer or a cover is not particularly limited,
and includes an embodiment which comprises injection molding the intermediate layer
composition or the cover composition directly onto the spherical core or the spherical
core formed with the intermediate layer, or an embodiment which comprises molding
the intermediate layer composition or the cover composition into a hollow-shell, covering
the spherical core or the spherical core formed with the intermediate layer with a
plurality of the hollow-shells and subjecting to the compression-molding (preferably
an embodiment which comprises molding the intermediate layer composition or the cover
composition into a half hollow-shell, covering the spherical core or the spherical
core formed with the intermediate layer with the two half hollow-shells, and subjecting
to the compression-molding).
[0126] When molding the intermediate layer or the cover in a compression molding method,
molding of the half shell can be performed by either compression molding method or
injection molding method, and the compression molding method is preferred. The compression-molding
of the intermediate layer composition or cover composition into half shell can be
carried out, for example, under a pressure of 1 MPa or more and 20 MPa or less at
a molding temperature of -20°C or more and 70°C or less relative to the flow beginning
temperature of the intermediate layer composition or the cover composition. By performing
the molding under the above conditions, a half shell having a uniform thickness can
be formed. The compression molding of half shells into the intermediate layer or cover
can be carried out, for example, under a molding pressure of 0.5 MPa or more and 25
MPa or less at a molding temperature of - 20°C or more and 70°C or less relative to
the flow beginning temperature of the intermediate layer composition or the cover
composition. By performing the molding under the above conditions, a golf ball cover
having a uniform thickness can be formed.
[0127] In the case of directly injection molding the intermediate layer composition or the
cover composition, the intermediate layer composition or the cover composition extruded
in the pellet form beforehand may be used for injection molding or the materials such
as the base resin components and the pigment may be dry blended, followed by directly
injection molding the blended material. It is preferred to use upper and lower molds
having a spherical cavity and pimples, wherein a part of the pimples also serves as
a retractable hold pin. When molding the intermediate layer or cover by injection
molding, the hold pin is protruded, the core is placed in, held with the hold pin,
and the intermediate layer composition or the cover composition which has been heated
and melted is charged and then cooled to obtain an intermediate layer or a cover.
For example, it is preferred that the intermediate layer composition or the cover
composition heated and melted at the temperature ranging from 200°C to 250°C is charged
into molds clamped under the pressure of 9 MPa to 15 MPa for 0.5 to 5 seconds, and
after cooling for 10 to 60 seconds, the molds are opened.
[0128] After the cover is molded, the golf ball body is ejected from the molds, and where
necessary the golf ball body is preferably subjected to surface treatments such as
deburring, cleaning, and sandblast. If desired, a paint film or a mark may be formed.
EXAMPLES
[0129] Hereinafter, the present invention will be described in detail by way of example.
The present invention is not limited to examples described below. Various changes
and modifications can be made without departing from the spirit and scope of the present
invention.
[Evaluation Methods]
(1) Slab Hardness (Shore D Hardness)
[0130] Sheets with a thickness of about 2 mm were produced by injection molding the intermediate
layer composition and cover composition, and stored at 23°C for two weeks. Three or
more of these sheets were stacked on one another so as not to be affected by the measuring
substrate on which the sheets were placed, and the hardness of the stack was measured
with a type P1 auto loading durometer manufactured by Kobunshi Keiki Co., Ltd., provided
with a Shore D type spring hardness tester prescribed in ASTM-D2240.
(2) Core Hardness Distribution (JIS-C hardness)
[0131] The core hardness was measured by the following method. The core hardness was obtained
by calculating the average of hardness measured at four points.
• Spherical core surface hardness (Hs2)
[0132] A type P1 auto loading durometer manufactured by Kobunshi Keiki Co., Ltd., provided
with a JIS-C type spring hardness tester was used. The JIS-C hardness measured at
the surface of the spherical core was adopted as the surface hardness (Hs2) of the
spherical core.
• Inner core layer surface hardness (Hs1)
[0133] The spherical core was cut into two hemispheres to obtain a cut plane. The surface
hardness (Hs1) of the inner core layer is JIS-C hardness measured in the region surrounded
by the following first and second circle on the cut plane. The first circle is defined
by the boundary between the inner core layer and the outer core layer. The second
circle is a concentric circle with the first circle and has a shorter radius than
the first circle by 10 % of the radius of the first circle. The radius of each circle
is as follows.
Radius of the first circle: r1=radius of the first circle
Radius of the second circle: r2=r1 x 0.9
• Outer core layer innermost point hardness (Hb)
[0134] The spherical core was cut into two hemispheres to obtain a cut plane. The surface
hardness (Hb) at the innermost point of the outer core layer is JIS-C hardness measured
in the region surrounded by the following first and third circle on the cut plane.
The first circle is defined by the boundary between the inner core layer and the outer
core layer. The third circle is a concentric circle with the first circle and has
a larger radius than the first circle by 10 % of the thickness of the outer core layer.
The radius of each circle is as follows.
Radius of the first circle: r1=radius of the first circle
Radius of the third circle: r3=r1 +(thickness of the outer core layer)x 0.1)
• Inner core layer central hardness (Ho) and hardness at points of 12.5% to 87.5%
in outer core layer
[0135] The spherical core was cut into two hemispheres to obtain a cut plane, and the JIS-C
hardness measured at the central point of the inner core layer is defined as the central
hardness (Ho) of the inner core layer. In addition, hardness was measured at predetermined
distances from the boundary point between the inner core layer and the outer core
layer.
(3) Compression Deformation Amount (mm)
[0136] A compression deformation amount of the core or golf ball (a shrinking amount of
the core or golf ball in the compression direction thereof), when applying a load
from an initial load of 98N to a final load of 1275N to the core or golf ball, was
measured.
(4) Coefficient of Restitution
[0137] A 198.4 g of metal cylindrical object was allowed to collide with each core or golf
ball at a speed of 45 m/sec, and the speeds of the cylindrical object and the core
or golf ball before and after the collision were measured. Based on these speeds and
the mass of each object, coefficient of restitution for each core or golf ball was
calculated. The measurement was conducted by using twelve samples for each core or
golf ball, and the average value was regarded as the coefficient of restitution for
the core or golf ball. Assuming that the coefficient of restitution of golf ball No.18
is defined as an index of 100.0, the coefficient of restitution of golf balls No.1
to No.27 are shown by converting the coefficient of restitution of each golf ball
into this index. Assuming that the coefficient of restitution of golf ball No.46 is
defined as an index of 100.0, the coefficient of restitution of golf balls No.28 to
No.56 are shown by converting the coefficient of restitution of each golf ball into
this index.
(5) Flight distance(m) and spin rate (rpm) on a driver shot
[0138] A titanium-head driver ("XXIO" manufactured by Dunlop sports, Shaft hardness: S,
loft angle: 10°) was installed on a swing robot M/C manufactured by TRUETEMPER Sports,
Inc. A golf ball was hit at a head speed of 45 m/sec, and the flight distance (the
distance from the launch point to the stop point) and the spin rate immediately after
hitting the golf ball were measured. This measurement was conducted ten times for
each golf ball, and the average value was adopted as the measurement value for the
golf ball. A sequence of photographs of the hit golf ball were taken for measuring
the spin rate (rpm) immediately after hitting the golf ball.
(6) Spin rate on Approach Shots
[0139] A sand wedge (CG15 forged wedge (52°), available from Cleveland Golf) was installed
on a swing robot M/C manufactured by TRUETEMPER Sports, Inc. A golf ball was hit at
a head speed of 21 m/sec, and a sequence of photographs of the hit golf balls were
taken for measuring the spin rate (rpm). The measurement was performed ten times for
each golf ball, and the average value is adopted as the spin rate (rpm).
(7) Durability
[0140] A titanium-head W#1 driver ("XXIO" manufactured by Dunlop sports, Shaft hardness:
S, loft angle: 10°) was installed on a swing robot M/C manufactured by TRUETEMPER
CO, and the head speed was set to 45 m/sec. Each golf ball was stored in a constant
temperature reservoir kept at the temperature of 23 °C for 12 hours. Immediately after
taking each golf ball out of the reservoir, they were repeatedly hit with the driver.
The number of hits required to break the golf ball was counted. This measurement was
conducted by using twelve golf balls for each golf ball. With respect to golf balls
No.1 to No.27, the number of hits for golf ball No. 1 was defined as an index of 100,
and the durability of each golf ball was represented by converting the number of hits
for each golf ball into this index. With respect to golf balls No.28 to No.56, the
number of hits for golf ball No. 28 was defined as an index of 100, and the durability
of each golf ball was represented by converting the number of hits for each golf ball
into this index. A greater index value indicates that the durability of the golf ball
is excellent.
[Production of Golf balls]
(1) Production of Inner Core layer
Rubber compositions No.1, 2
[0141] The rubber compositions having formulations shown in Table 3 were kneaded with a
kneading roll and pressed in upper and lower molds, each having a hemispherical cavity
to prepare the spherical inner cores. The heat-pressing was conducted under the conditions
shown in Tables 6 to 11.
Resin compositions No. 18 to 21
[0142] The blending materials shown in Table 3 were dry blended, followed by mixing with
a twin-screw kneading extruder to extrude the blended material in the strand form
into the cool water. The extruded strand was cut with a pelletizer to prepare an inner
core layer composition in the form of pellet. Extrusion was performed in the following
conditions: screw diameter=45 mm; screw revolutions=200 rpm; and screw L/D=35. The
mixtures were heated to a temperature in a range from 160°C to 230°C at a die position
of the extruder. The obtained inner core layer composition in the form of pellet was
injection molded at a temperature of 220°C to prepare spherical inner cores.
(2) Production of Spherical Cores
[0143] The rubber compositions shown in table 3 were kneaded and molded into half shells.
Molding of half shells was conducted by charging a pellet of the rubber composition
into each of the depressed part of the lower mold for molding half shells, and applying
pressure to mold half shells. Compression molding was conducted at the temperature
of 30 °C for 1 minute under the molding pressure of 10 MPa. The inner core layers
obtained above were covered with two half shells. The inner core layers covered with
two half shells were placed in the molds composed of upper mold and lower mold each
having a spherical cavity and heat-pressed under the conditions shown in tables 6
to 11 to prepare the spherical cores consisting of the inner core layer and the outer
core layer covering the inner core layer. It is noted that the blending amount of
barium sulfate was adjusted to make the golf ball have a mass of 45.6g.
BR-730: a high-cis polybutadiene (cis-1,4 bond content = 96 mass %, 1,2-vinyl bond
content = 1.3 mass %, Moony viscosity (ML1+4 (100 °C) =55, molecular weight distribution (Mw/Mn) =3) available from JSR Corporation
Sanceler SR: zinc acrylate (product of 10 mass % stearic acid coating) available from
Sanshin Chemical Industry Co., Ltd.
ZN-DA90S: Zinc acrylate (product of 10 mass % zinc stearate coating)available from
Sanshin Chemical Industry Co., Ltd.
Zinc oxide: "Ginrei R" manufactured by Toho Zinc Co., Ltd.
Barium sulfate: "Barium sulfate BD" manufactured by Sakai Chemical Industry Co., Ltd.,
adjustment was made such that the finally obtained golf ball had a mass of 45.6 g.
2-thionaphthol: manufactured by Tokyo Chemical Industry Co., Ltd. Bispentabromophenyldisulfide:
manufactured by Kawaguchi Chemical Industry Co., Ltd.
Dicumyl peroxide: "Percumyl (registered trademark) D" manufactured by NOF Corporation.
Zinc octanoate: manufactured by Mitsuwa Chemicals Co., Ltd.
Zinc stearate: manufactured by Wako Pure Chemical Industries, Ltd.
Zinc myristate: manufactured by Wako Pure Chemical Industries, Ltd.
Himilan AM7327: Zinc ion neutralized ethylene-methacrylic acid-butyl acrylate ternary
copolymer ionomer resin available from Du Pont-Mitsui Polychemicals Co., Ltd.
Nucrel AN4319: Ethylene-methacrylic acid-butyl acrylate ternary copolymer available
from Du Pont-Mitsui Polychemicals Co., Ltd.
Basic magnesium oleate: available from Nitto Kasei Kogyo K.K. (metal content: 1.4
mol %)
Basic magnesium oleate: available from Nitto Kasei Kogyo K.K. (metal content: 1.7
mol %)
Magnesium hydroxide: available from Wako Pure Chemical Industries Ltd.
Oleylbetaine (oleyldimethylaminoacetic acid betaine): a purified preparation of "Chembetaine
OL" available from The Lubrizol Corporation (water and salt are removed)
Nocrac 200: 2,6-di-t-butyl-4-methylphenol available from Ouchi Shinko Chemical Industrial
Co., Ltd.
(3) Preparation of Intermediate Layer Composition and Cover Composition
[0144] The blending materials shown in Tables 4 to 5 were mixed with a twin-screw kneading
extruder to prepare an intermediate layer composition and cover composition in the
form of pellet. Extrusion was conducted in the following conditions: screw diameter=45
mm; screw revolutions=200 rpm; and screw L/D=35. The mixtures were heated to a temperature
in a range from 160 °C to 230 °C at a die position of the extruder.
Surlyn 8945: a sodium ion neutralized ethylene-methacrylic acid copolymer ionomer
resin available from E.I. du Pont de Nemours and Company.
Himilan AM7329: a zinc ion neutralized ethylene-methacrylic acid copolymer ionomer
resin available from Du Pont-Mitsui Polychemicals Co., Ltd.
Rabalon T3221C: Styrene elastomer available from Mitsubishi Chemical Corporation.
Titanium dioxide: Ishihara Sangyo Kaisha, Ltd.
Elastollan NY82A: Polyurethane elastomer available from BASF Japan Co.
Elastollan NY85A: Polyurethane elastomer available from BASF Japan Co.
Elastollan NY90A: Polyurethane elastomer available from BASF Japan Co.
Elastollan NY97A: Polyurethane elastomer available from BASF Japan Co.
Tinuvin 770: a hindered amine stabilizer available from BSFA Japan Ltd.
(4) Production of Golf Ball Body
[0145] Intermediate layer for 4 piece golf ball No. 1 to No.27
[0146] The intermediate layer compositions obtained above were injection-molded onto the
spherical cores to form the intermediate layers. When molding the intermediate layer,
the hold pins were protruded, the cores were placed in the molds and held with the
protruded hold pins, the intermediate layer compositions heated at 260°C was charged
into the molds clamped at a pressure of 80 tons within 0.3 seconds, and cooled for
30 seconds. Then, the molds were opened, and the spheres covered with the intermediate
layer were ejected.
Intermediate layer for 5 piece golf ball No.28 to No.56
First intermediate layer
[0147] The intermediate layer compositions obtained above were injection-molded onto the
spherical cores to form the first intermediate layers. When molding the first intermediate
layer, the hold pins were protruded, the spherical cores were placed in the molds
and held with the protruded hold pins, the intermediate layer compositions heated
at 260°C was charged into the molds clamped at a pressure of 80 tons within 0.3 seconds,
and cooled for 30 seconds. Then, the molds were opened, and the spheres covered with
the first intermediate layer were ejected.
Second intermediate layer
[0148] The intermediate layer compositions obtained above were injection-molded onto the
spheres covered with the first intermediate layer to form the second intermediate
layers covering the spheres covered with the first intermediate layers.
[0149] When molding the second intermediate layer, the hold pins were protruded, the spheres
covered with the first intermediate layers were placed in the molds and held with
the protruded hold pins, the intermediate layer compositions heated at 260°C was charged
into the molds clamped at a pressure of 80 tons within 0.3 seconds, and cooled for
30 seconds. Then, the molds were opened, and the spheres covered with the intermediate
layer were ejected.
Reinforcing layer
[0150] The reinforcing layer was formed by applying a two-component curing type thermosetting
resin to the molded intermediate layer. As the two-component curing type thermosetting
resin, a paint composition including a two-component curing type epoxy resin as a
base polymer was used. The base material liquid of this paint composition includes
30 parts by mass of a bisphenol A type solid epoxy resin and 70 parts by mass of a
solvent. The curing agent liquid of this paint composition includes 40 parts by mass
of a modified polyamide amine, 5 parts by mass of titanium oxide, and 55 parts by
mass of a solvent. The mass ratio of the base material liquid to the curing agent
liquid is 1/1. This paint composition was applied to the surface of the intermediate
layer with a spray gun, and maintained at 23 °C for 12 hours to obtain a reinforcing
layer with a thickness of 6 µm.
[0151] Compression molding of half shells was conducted by, charging one pellet of the cover
composition obtained as described above into each of depressed parts of lower molds
for molding half shells, and applying pressure to mold half shells. Compression molding
was conducted at a temperature of 160°C for 2 minutes under a molding pressure of
11 MPa. The spheres covered with the intermediate layer and formed with the reinforcing
layer were covered with the two half shells in a concentric manner, placed in the
molds having a plurality of pimples on the surface of the cavity thereof. Compression
molding was conducted at a temperature of 150 °C for 3 minutes under a molding pressure
of 13 MPa. The molded cover was formed with a plurality of dimples which have inverted
shape of the pimples.
Paint Film
[0153] As apparent from the results of tables 6 to 8, the golf balls where a hardness difference
(Hs1-Ho) is 5 or less in JIS-C hardness; the outer core layer is such that R
2 of a linear approximation curve is 0.95 or higher, the intermediate layer has a slab
hardness (Hm) which is higher than a slab hardness (Hc) of the cover each have a great
flight distance (241 m or more) on driver shots, high spin rate (6000 rpm or more)
on approach shots and excellent durability.
[0154] The golf balls No.1, 2 and 7 are the cases where the outer core layer is such that
R
2 of a linear approximation curve is less than 0.95. Although the spin rate on approach
shots was high, the flight distance on driver shots was short. The golf ball No.17
is the case where the slab hardness (Hm) of the intermediate layer is lower than the
slab hardness (Hc) of the cover. Although the flight distance on driver shots was
great, the spin rate on approach shots was low. The golf ball No.18 is the case where
the hardness difference (Hs1-Ho) is as large as 10 in JIS-C hardness. Although the
spin rate on approach shots was high, the flight distance on driver shots was short.
[0155] As apparent from the results of tables 9 to 11, the golf balls where a hardness difference
(Hs1-Ho) is 5 or less in JIS-C hardness; the outer core layer is such that R
2 of a linear approximation curve is 0.95 or higher, the first intermediate layer has
a slab hardness (Hm1) which is lower than the slab hardness (Hm2) of the second intermediate
layer, and the second intermediate layer has a slab hardness (Hm2) which is higher
than a slab hardness (Hc) of the cover each have a great flight distance on driver
shots, high spin rate on approach shots and excellent durability.
[0156] The golf balls No.28, 29 and 34 are the cases where the outer core layer is such
that R
2 of a linear approximation curve is less than 0.95. Although the spin rates on approach
shots were high, the flight distances on driver shots were short. The golf ball No.44
is the case where the slab hardness (Hm) of the intermediate layer is lower than the
slab hardness (Hc) of the cover. Although the flight distance on driver shots was
great, the spin rate on approach shots was low. The golf ball No.45 is the case where
the first intermediate layer has the slab hardness (Hm1) which is higher than the
slab hardness (Hm2) of the second intermediate layer. Although the spin rate on approach
shots was high, the flight distance was short due to the high spin rate on driver
shots. The golf ball No.46 is the case where the hardness difference (Hs1-Ho) is as
large as 10 in JIS-C hardness. Although the spin rate on approach shots was high,
the flight distance on driver shots was short. The golf ball No. 59 traveled a great
distance on driver shots and produced a high spin rate on approach shots. However,
if compared with the golf ball having the intermediate layer composed of two or more
layers, the durability was lowered.
[0157] The golf ball of the present invention travels a great flight distance, and has an
excellent approach performance and durability.